JP2003251445A - Method for controlling changeover of molten metal surface level meter in mold at the time of starting continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smoothly shift a measurement of molten metal surface level from a thermo-couple type level meter to an eddy current type level meter when a continuous casting is automatically started. <P>SOLUTION: A value until the molten metal surface level in a mold reaches the lower limit position in the measuring range set to the eddy current type meter after starting pouring of the molten metal into the mold, is made to zero, and a value until the output of the level meter becomes a prescribed value from the lower limit position, is increased from zero to 1, and when the output of the lever meter becomes not lower than the prescribed value, a value is made to 1. The molten surface level Lc calculated with the formula, Lc=WE(L)×Le+WT(L)×Lt, containing WE weight given with a function of the molten metal surface level L and WT weight given with (1-WE), is used as the molten metal surface level in the mold. Wherein, L is the actual molten metal surface level; Le is the measured value of the molten metal surface level with the eddy current type level meter; and Lt is the measured value of the molten metal surface level with the thermo-coupled type level meter. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus having a plurality of types of molten metal level gauges in a mold, and at the start of casting when continuously casting molten metal, the molten metal level gauges for non-steady-state The present invention relates to a molten metal level gauge switching control method at the start of continuous casting, which is suitable for smooth switching to a molten metal level gauge for control.

[0002]

2. Description of the Related Art In a continuous casting facility for molten metal, in order to precisely control the level of molten metal in the mold during steady casting,
Eddy current level meters are mainly used. The level of the molten metal surface can be measured accurately and stably by this eddy current level meter from the bottom surface of the eddy current sensor to a maximum of 150 mm to 200
The range is about mm. On the other hand, the mold of the continuous casting equipment, especially the mold of the slab continuous casting machine, has a height of about 900 mm. When starting casting with a continuous casting machine, a dummy bar is inserted from below to prevent leakage of molten metal downward, but the upper end of this dummy bar is usually at the middle of the mold height. It is put in the position of degree. Therefore, when molten metal is poured into the mold from the tundish at the start of casting, the molten metal begins to accumulate in the mold and the molten metal surface gradually rises to about 300
The rise of the molten metal surface between mm and 250 mm cannot be measured by the eddy current level meter.

Therefore, until the level of the molten metal in the mold begins to rise at the start of casting and the level of the molten metal can be measured by the vortex flow level meter, the molten metal level is detected by a thermocouple and the thermocouple level meter is used. Alternatively, by visually detecting the molten metal level, the molten metal level in the mold outside the measurement range of the eddy current level meter is grasped. Therefore, when the molten metal level reaches the measurable range of the eddy current level meter, it is necessary to switch the thermocouple level meter etc. used to the eddy current type level meter. It was necessary to switch.

The conventional techniques as described above have the following problems.

(1) In the case of manual intervention for switching the level meter, the visual manual operation is inferior in controllability to the automatic control with a short control cycle, and there is a difference or variation in individual skill. This has been a factor causing fluctuations in the level of the molten metal surface, deteriorating the quality, and causing cast pieces that cannot be handled as products. In addition, the manual intervention work itself imposes a burden on the worker, which hinders labor saving.

(2) Using a thermocouple level meter, after raising the molten metal level in the mold to a steady level, automatic slab extraction is started and the molten metal level is controlled to reach a predetermined range. In the so-called auto-start method that starts, when measuring with an eddy current level meter in the process of raising the molten metal surface and stabilizing it to a mold level that allows steady control due to the limits of accuracy and measurement delay time of the thermocouple method. Compared with the above, the fluctuation of the molten metal surface was large, and the quality was deteriorated.

Therefore, in order to solve the above problems, in Japanese Patent No. 3221990, when the level of the molten metal in the mold is low, the measured value from the thermocouple type level meter is output to output the molten metal in the mold. When the level is high, the measured value from the electromagnetic level meter (eddy current level meter) shall be output, and when switching between the two level meters, the measured value of the level meter used before switching and the value after switching It is proposed to obtain the difference between the measured values of the level meter used and add this difference to the measured value of the level meter used after switching as a correction value that gradually changes within the mold variation allowable level range. ing.

[0008]

However, in the method described in the above patent publication, ideally it was expected that the transition from the thermocouple level meter to the eddy current level meter would be made continuously, but in reality, However, it still had the following problems.

That is, since there is a variation in the rate of rise of the molten metal at the time of automatic start, the switching from the thermocouple type to the vortex type may be delayed, which may cause fluctuations in the molten metal and overshoot. If the level of the molten metal changes so much that it once enters the eddy current type measurement range and then falls outside the eddy current type measurement range, a vortex flow level meter is used outside the measurement range. There is a situation in which it is impossible to add up as a total and output. Further, there arises a problem when the sensitivity of the thermocouple near the level of the molten metal in the mold where the thermocouple type level meter and the eddy current type level meter are switched is deteriorated or when water is flooded. In other words, if the thermocouple near the mold level that switches between the thermocouple type and the eddy current type is defective and the mold level indicated value (measured value) by the thermocouple type level meter does not rise above a certain value, the thermocouple type It becomes impossible to use a method of automatically switching to the eddy current type when the paired type instruction value exceeds a predetermined threshold value. When switching is performed at the timing when the indicated value of the eddy current level meter reaches the measurable range, the indicated value of the thermocouple level meter is changed to the indicated value for the interval of one or more thermocouples. Since there is a difference, if you try to switch by the correction value that does not affect the control, there will be a delay time by that amount and an error as a level meter will occur. Therefore, the fluctuation of the molten metal surface occurs until the molten metal surface after the overshoot is stabilized.

The present invention has been made in order to solve the above-mentioned conventional problems. At the start of casting in continuous casting, in particular, at the time of automatic start, the measured value of the molten metal level from the thermocouple type level meter to the vortex type level meter is measured. It is an object of the present invention to provide a control technology for switching the level gauge which enables smooth and automatic transition without causing the above-mentioned operational difficulties.

[0011]

The present invention is set in a first level gauge used for measuring the level of the level during steady control of the level in the mold, and is set in the first level meter. When starting continuous casting of molten metal using a continuous casting equipment having a second level gauge capable of measuring the level of the molten metal in a range overlapping the measurement range and a lower range,
After starting the injection of the molten metal into the mold, it is zero until the level of the molten metal in the mold reaches the lower limit position of the measurement range set in the first molten metal level gauge, and the output of the same level meter from the lower limit position. It increases from zero to 1 until it reaches a predetermined value, and becomes 1 when the output of the same level meter is above the predetermined value, and is given by (1-WE) The following equation Lc = WE (L) × Le + WT (L) × Lt, where Lc is a calculated value (mm) of the molten metal level in the mold,
L is the actual melt level (mm), Le is the melt level measured by the first level meter (mm), Lt is the melt level measured by the second level meter (mm), and WE is the first level. , And WT is the weight (-) of the second level meter. The above-mentioned problem is solved by using the molten metal level Lc calculated according to () as the molten metal level in the mold.

In the present invention, it is preferable to use the measured value Le by the first melt level meter instead of the actual melt level L. In the present invention, the first
It is preferable to use an eddy current type level meter as the molten metal level gauge and a thermocouple type level meter as the second molten metal level meter.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

In the continuous casting equipment to which the present invention is applied, molten metal is poured into a vertically open mold from above, and at least a slab whose surface is solidified by heat removal to the mold is continuously drawn from below. It is a continuous casting equipment for molds. Slab continuous casting equipment, roughly classified according to the cross-sectional shape of the cast slab,
Bloom continuous casting equipment, billet continuous casting equipment, etc. are available, but both are suitable. Further, there are a vertical type continuous casting equipment, a vertical bending type continuous casting equipment, a full-curve type continuous casting equipment, and the like, which are roughly classified according to how the slab is drawn out, and the present invention is applicable to any of these continuous casting equipments.

However, it is necessary to provide two types of level gauges as the level gauge in the mold. One of them is used for steady level control of the molten metal level. Steady level control of the molten metal level means the start of casting, the end of casting, etc.
This is the control of the molten metal level during the casting period when the molten metal surface is almost stable, except when the molten metal position changes extremely. That is,
In order to stabilize the quality of the cast slab as high as possible, the injection speed of molten metal from the tundish into the mold and the drawing speed of the slab should be adjusted so that the molten metal level stabilizes at the target level. It is important to control. For this purpose, it is necessary to measure the level of the molten metal precisely, and for this purpose, the eddy current level meter is now widely used. However, it is known that this swirl level meter has a relatively narrow range of level height that can be measured.

The other level meter is capable of detecting a low level metal level which cannot be measured by the level meter for steady control. In many cases, the thermocouple is embedded in the mold wall portion at intervals in the height direction, and the molten metal surface position is grasped by measuring the temperature change of the copper plate constituting the inner wall of the mold by these thermocouples, A so-called thermocouple level meter is used.

An example of a preferred level meter arrangement for practicing the present invention is shown in FIG. In FIG. 1, the upper half of the mold 10 and the molten steel M injected into the mold 10 from a tundish (not shown) through a dipping nozzle 12.
The relationship with and is schematically shown. The eddy current sensor, which is the main body of the eddy current level meter 14, is arranged in a space inside the mold from above the mold 10 and above the molten metal surface at a predetermined distance.

On the other hand, a plurality of thermocouple type level meters 16 are provided at predetermined intervals in the height direction on the front side copper mold plate (for example, short side copper plate in a slab continuous casting machine) which is omitted in FIG. The thermocouple 16A is embedded. FIG. 2 shows the installation state of each thermocouple 16A constituting the thermocouple type level meter 16 in a vertical cross section of the corresponding mold short side wall.

As shown in FIG. 2, a mold 10 for casting by injecting molten steel M into a molten steel M by growing a solidified shell Mc is composed of an inner wall copper plate 10A and an outer back frame 10B. The tip of the thermocouple 16A is arranged so as to be inserted into the inside of the copper plate 10A. As this thermocouple level meter 16, for example, 23
It can be formed by embedding a thermocouple 16A of a book at intervals of 20 mm. In addition, the measurement range of the molten metal level by the thermocouple is arranged so as to partially overlap with the measurement range by the eddy current sensor. This is because, as will be described later, in the present invention, a weighted average of both measured values is used as a measured value of the molten metal level in a certain height range.

In FIG. 3, at the start of casting (at the time of automatic start)
An example of the rise of the molten metal level (M / D) in the mold and the measurement range of the thermocouple type level meter 16 and the eddy current type level meter 14 are shown. In the present invention, the measurement result L of the thermocouple type level meter 16
Using t and the measurement result Le of the eddy current level meter 14, the weight level shown in FIG. 4 is used to calculate the molten metal level in the mold by the following calculation formula (1).

[0021]       Lc = WE (L) × Le + WT (L) × Lt (1)

Here, L is the actual molten metal level (mm),
Le is the surface level measurement value (m
m) and Lt are measured values (mm) of the molten metal level by the thermocouple type level meter, WT (L) is the weight of the thermocouple type level meter (-), and WE (L) is the weight of the eddy current type level meter (-). ), L
c is a calculated value (mm) of the molten metal level in the mold. In addition,
WT (L) = 1-WE (L).

A predetermined lower limit position Le (min) provided in the measurable range by the eddy current level meter 14 (this is not shown, but may be the lower limit position as the measurable range, or to some extent from this. WE (L) is set to zero below the upper level. That is, the measured value of the thermocouple type level meter 16 is exclusively used as the value of the molten metal level.

In the range from the lower limit position until the output of the eddy current level meter 14 reaches a predetermined value, WE (L) is a value that changes from zero to 1 according to the molten metal level L. However, since the actual molten metal level L cannot be known, the measured value Lt by the thermocouple type level meter 16 or the measured value Le by the eddy current type level meter 14 is used instead for calculation. As described above, the thermocouple type level meter may have a problem such as a defect of each thermocouple or a difference in sensitivity. Therefore, when the measurement by the eddy current type level meter becomes possible, the measured value Le is preferably used. Good to do. That is, in this case,
The molten metal level is calculated by the following formula (2) instead of formula (1).

[0025]       Lc = WE (Le) × Le + WT (Le) × Lt (2)

Also in this case, WT (Le) = 1-WE
There is no change in the relationship (Le). And
Although FIG. 4 is an example in which WE (Le) is given as a linear function with respect to Le, WE (Le) does not necessarily have to be a linear function of Le, and the response of the thermocouple type level meter,
Based on the sensitivity of the vortex flow level meter, or the characteristics of the whole flow rate control system of the molten metal injection system from the tundish and the molten steel from the tundish, zero at the lower limit of Le mentioned above,
1 when the output of the eddy current level meter reaches the above specified value
It may be any function that increases until

With the above structure, the present invention has the following advantages over the invention described in the above-mentioned Japanese Patent No. 3221990.

(1) Since a plurality of level meters can be automatically switched, the casting start work can be continuously controlled with automatic control, so that it is possible to prevent variations in the mold level and, as a result, to improve the quality. It is possible to improve the number of cast pieces that can be handled as a product, and reduce the workload of manual intervention.

(2) The thermocouple type level meter 16 raises the molten metal surface to the measurement range of the eddy current type level meter, and then the eddy current type level meter 14 with high accuracy continuously measures and continues automatic control. Therefore, in the continuous casting equipment of the auto start system, the fluctuation of the molten metal surface can be suppressed, the overshoot can be prevented, and the quality can be improved.

(3) Conventionally, after the thermocouple type level meter is switched to the eddy current type level meter, the measured value of the eddy current type level meter is set at a constant time interval until a certain time elapses. Although the difference is taken into consideration as the correction value, in actuality the level of rising surface of the molten metal is not constant in many cases but varies, so in such a case a delay in control response may occur. However, according to the present invention, when the molten metal level falls within the measurement range of the vortex type level meter 14, it is possible to switch to the eddy current type level meter irrespective of the passage of time, so there is a fluctuation in the molten metal level rise speed. Also, it is possible to eliminate the delay of the control response to it, and it is possible to eliminate the factors of fluctuations in the molten metal surface and overshoot.

(4) Further, in the prior art, after the molten metal level meter was switched to the vortex type level meter after a certain period of time, the fluctuation of the molten metal level was large and the temperature temporarily entered the measurement range of the vortex type level meter. After that, even when the temperature falls outside the measurement range again, the output of the eddy current level meter outside the measurement range is used, and the calculation for controlling the level of the molten metal is impossible. Such a problem does not occur because the measurement value of the eddy current level meter 14 is automatically switched to the measurement value of the thermocouple level meter 16 according to the surface level. Therefore, the automatic control can be smoothly and continuously continued.

(5) Further, in the prior art, a problem occurs when the thermocouple near the molten metal level for switching between the thermocouple type and the vortex type is defective, but in the present invention, the indication of the thermocouple type level meter is given. Even if there is a difference in the measured value of the molten metal level by the distance between one or more thermocouples, when the molten metal level reaches the measurement range of the eddy current level meter, the weight of the measured value of the eddy current level meter is weighted. Since the value can be gradually and continuously increased from zero, the value of the molten metal level according to the equation (1) can be continuously converged to the measurement value of the eddy current level meter 14 without a time delay. As a result, it is possible to reduce the error of the molten metal level meter, suppress the overshoot of the actual molten metal surface, and suppress the fluctuation of the molten metal surface.

[0033]

[Example] The present invention and the above-mentioned conventional example are applied to the operation of continuously casting SUS304 stainless steel using a slab continuous casting facility having an inner dimension of a width of 600 to 1650 mm, a thickness of 200 and 260 mm, and a height of 900 mm. I did an experiment. The arrangement of the thermocouple and the arrangement of the eddy current type level meter are as shown in FIGS. 1 and 2. Further, as shown in FIG. 3, the measuring range of the thermocouple type level meter is a range of 450 mm from the center of the mold height direction (the position marked −450 mm in the drawing) to the upper end of the mold. The measurement range of the eddy current level meter is a range of 150 mm from the upper end of the mold to a position 150 mm below (the position marked -150 mm in the figure). In FIG. 3, ML0 represents a steady control position at the molten metal level, and P / R speed represents a withdrawal speed of the slab.

In applying the conventional example as a comparative example, when the measured value of the thermocouple type level meter becomes -150 mm, it is switched to the measured value of the eddy current type level meter, and then 1
A correction value was calculated from the difference between the measured value of the thermocouple type level meter and the measured value of the eddy current type level meter over 30 seconds in every second, and the measured value of the eddy current type level meter was corrected.

On the other hand, in the example of the present invention, the surface level is -15.
When WE was 0 mm or less, WE was 0, and when the molten metal level was -125 mm or more, WE was 1. During that period, WE was set to a function that linearly changes with respect to the molten metal level. Here, as the molten metal level for WE calculation, the measured value Le of the eddy current level meter was used.

In the comparative example and the example of the present invention, as described above, 100 heats were cast, and the bottommost portion of the produced slab (that is, the slab corresponding to the start of casting, which is a portion immediately after the dummy bar) ) Quality was investigated. As a result, the bottom crop length, which was cut off because it could not be used as a product due to defects in oscillation marks on the surface of the slab caused by defects in the molten metal level control, and defects such as bleeding, averaged 5. While it was 4m,
In the example of the present invention, it was possible to reduce the average to 2.3 m.

The present invention has been specifically described above, but the present invention is not limited to the one shown in the above embodiment, and various modifications can be made without departing from the spirit of the invention.

[0038]

As described in detail above, according to the present invention, a range overlapping the measurement range of the first level gauge used for steady control of the level in the mold and the level control level meter for steady control. When starting continuous casting of molten metal using a continuous casting facility having a second molten metal level gauge capable of measuring a range lower than the above range, it is possible to smoothly and automatically switch between the measured values of both. Therefore, it is possible to prevent an overshoot from occurring in the level control of the molten metal even if there is a fluctuation in the rising speed of the molten metal in the mold, and to measure continuously even if the second level meter with a long measuring range is defective. As a result, fluctuations in the molten metal surface can be suppressed, so that the excellent effect of improving the quality of the cast piece and increasing the cast piece portion that can be handled as a product can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic perspective view schematically showing a mold to which an embodiment according to the present invention is applied.

FIG. 2 is a partial cross-sectional view of a mold that schematically shows the installation state of a thermocouple-type level gauge

FIG. 3 is a diagram showing the relationship between the molten metal level and the measuring range of the level meter.

FIG. 4 is a diagram showing a relationship between a molten metal level and a weight function of a level meter.

[Explanation of symbols]

10 ... Mold 14 ... Eddy current level meter 16 ... Thermocouple type level meter

Claims (3)

[Claims] 1. A first molten metal level meter used for measuring the molten metal level at the time of steady control of the molten metal level in the mold, and a range overlapping with the measurement range set in the first molten metal level meter and the same. When initiating continuous casting of molten metal using a continuous casting facility having a second molten metal level meter capable of measuring the molten metal level in a lower range, after injecting molten metal into the mold, Zero until the surface level reaches the lower limit position of the measurement range set in the first molten metal level meter, increases from zero to 1 until the output of the same level meter reaches a predetermined value from the lower limit position, The following equation Lc = WE (L, which includes a weight WE given as a function of the molten metal level L and a weight WT given as (1-WE), which is 1 when the output of the same level meter is equal to or higher than the predetermined value. ) × Le + WT (L) × Lt (where Lc is in the mold Calculated surface level (mm), L is the actual melt surface level (mm), Le is molten metal surface level measured by the first level meter (m
m), Lt is the level measured by the second level meter (m
m), WE is the weight (-) of the first level meter, and WT is the weight (-) of the second level meter. ) The molten metal level Lc calculated by the above is used as the molten metal level in the mold, and the molten metal level gauge switching control method at the start of continuous casting is characterized. 2. In determining the weights WE and WT,
The method according to claim 1, wherein the measured value Le by the first level gauge is used in place of the actual level L. 3. A vortex type level meter is used as the first molten metal level gauge, and a thermocouple type level meter is used as the second molten metal level gauge. A method for controlling switching of a molten metal level gauge at the start of continuous casting described in the above.