JPH06238412A - Device and method for controlling molten metal surface height at the time of continuously casting - Google Patents

Abstract

PURPOSE:To prevent the overflow caused by rapid riding of molten steel surface frequently generate at the initial stage of casting by precisely measuring the molten steel surface height in a continuous casting mold from the initial stage of the casting. CONSTITUTION:A molten metal surface height control device is constituted by combining an electrode type molten metal surface height meter 11 having four sets of electrodes 12a-12d composed of two lead wires and arranged on the inner surface or its neighborhood of the continuous casting mold 1 while mutually separated in the casting direction at these tip parts of the electrodes 12a-12d and a device for adjusting the opening degree of a sliding nozzle in a tundish arranged above the continuous casting mold 1 based on the outputted signal from the electrode type molten metal surface height meter 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention In the continuous casting process of molten metal, the present invention relates to the level of molten metal at the initial stage of casting, that is, the level of molten metal in the continuous casting mold, which has been conventionally set. During continuous casting, the level of the molten metal can be detected with high accuracy and automatically controlled from a time that is too low to be measured by a meter (when the drawing speed is constant immediately after the continuous casting slab is drawn by the dummy bar). The present invention relates to a level control device and a control method.

[0002]

2. Description of the Related Art In continuous casting of molten metal (hereinafter, "molten steel" will be described as an example of "molten metal" in the present specification), as shown in FIG. Molten steel contained in a tundish 3 is cast through a submerged nozzle 2 immersed in a water-cooled continuous casting mold 1 to form a continuous casting mold 1 and a water cooling nozzle.
The continuously cast slab 4 which is cooled and solidified by (not shown) is pulled out by a pinch roll (not shown) installed below.

A known operating problem in this continuous casting process is breakout in which the solidified shell of the continuously cast slab 4 is broken and the unsolidified molten steel flows out.
In addition to breakout, it is known that the unsolidified molten steel in the continuous casting mold 1 overflows from the upper part of the continuous casting mold 1.

This is a phenomenon that occurs when the amount of molten steel supplied from the tundish 3 is larger than the drawing speed of the rapidly cast and solidified continuous cast slab 4, which lowers the yield and the productivity. It causes damage.

Therefore, it is generally necessary to control the molten steel level in the continuous casting mold within a predetermined range so that the molten steel in the continuous casting mold does not overflow. The control of the molten steel level in the continuous casting mold has been performed for a long time.For example, γ-rays are emitted from cobalt 60 and the molten steel level is detected by measuring the γ-rays attenuated by the molten steel. The level of molten steel has been controlled by the Ri method.

Also in the conventional continuous casting apparatus shown in FIG. 5, a molten metal level gauge 5 is installed above the continuous casting mold 1. A swirl type distance meter is normally used for this level gauge 5, and the distance at which the level height can be measured while maintaining the measurement accuracy of ± 3.0 mm (distance between level and distance meter) is Up to 15
Since the height is 0 mm, the level gauge 5 must be installed considerably above the normal position of the level. Therefore, when the molten metal is held in the mold at the beginning of casting in the continuous casting process, the molten metal level is located below the measurable range of the molten metal level gauge 5, so the molten metal level gauge 5 should be used. However, while maintaining the opening of the sliding nozzle 7 of the tundish 3 at a predetermined value and empirically controlling the supply amount of molten steel, the level It was decided to detect and control the height of the molten metal surface by a total of 5. In addition,
In the device shown in the figure, the signal from the bath level gauge 5 is output to the microcomputer, converted into the opening signal of the sliding nozzle 7 by the DDC (Direct Digital Controller) 8, and the hydraulic servo amplifier 9 and the hydraulic servo are used.
The opening of the sliding nozzle 7 was controlled via 10.

In recent years, for example, in CAMP-ISIJ (Materials and Processes, Vol. 5, p. 294), in order to control the level of the molten metal from the start of casting to the steady state, the inner circumference of the continuous casting mold is A plurality of thermocouples were embedded in the arranged Cu plate so as to have a constant pitch in the casting direction, and from the temperature transition obtained from the measured values from these thermocouples, the molten steel level in the continuous casting mold 1 Techniques for detecting height are introduced. Hereinafter, this technique will be described in detail with reference to FIGS. 6 to 8.

In recent years, as the continuous casting mold has been made smaller in cross-section, higher precision has been required to control the height of the molten metal surface. For the purpose of eliminating the poor response (heat conduction delay), which is the weak point of detection, as shown in Fig. 6, the level of the surface (when the surface is rising, when the surface is stopped or when the surface is descending), Attention was paid to the correspondence with the positional and temporal change Δq of the amount of heat transferred to the continuous casting mold. In the figure, Δq> 0 indicates an increase in the amount of heat transferred to the continuous casting mold, and Δq <0 indicates a decrease in the amount of heat transferred to the continuous casting mold.

When the molten metal rises, the casting speed is low and
Although the contact time with the Cu plate is longer in the upper part of the continuous casting mold, the temperature of molten steel is higher in the upper part of the continuous casting mold.
The distribution of Δq is as shown in (a). When the molten metal is descending, the casting speed is high and the contact time between the molten steel and the Cu plate is longer in the lower part, but since the molten steel is hotter in the lower part of the continuous casting mold, there is a distribution of Δq as shown in Fig. 6 (c). Become. Further, when the molten metal is stopped, since the pouring speed and the pouring speed are equal, the lower the Cu plate is, the easier it is to cool, and the distribution of Δq shown in FIG. In each case, the pouring temperature exceeds the heat removal amount of the Cu plate.

The relationship between these molten metal surface states and the positional and temporal changes Δq in the amount of heat transferred to the continuous casting mold is as shown in FIGS. 6 (a) to 6 (c). When the surface rises, the bath height corresponds to the boundary position between Δq and 0, and when the bath surface descends, the bath height corresponds to the boundary position between Δq and negative, and when the bath surface stops. Then, due to the growth of the solidified shell Δ
The level of the molten metal corresponds to the boundary position between q and 0.

Then, the positional / temporal change Δ in the amount of conduction heat
The change in q is represented by the temperature change amount ΔTi for each sampling period Δθ.
= [Ti (θ) -Ti (θ-Δθ)], and the molten steel surface height is calculated from the distribution in the continuous casting mold.

The main procedure for this calculation will be described with reference to FIG. 7 (a) and 7 (b) respectively,
6 is a graph showing respective values at the sampling position with respect to the temperature change amount ΔTi for each sampling cycle Δθ, and the ratio ΔTi / ΔL of the temperature change amount ΔTi and the casting direction distance ΔL of the sampling position. In FIG. 7, the upper part of the Cu plate is kept warm by the solidified shell as it goes downward, but when the solidified shell begins to solidify,
Heat is removed by the Cu plate. Also, in the lower part of the Cu plate, heat is removed by the Cu plate through the semi-solidified shell as it goes downward,
As it goes further down, it is kept warm by the solidified shell
Prevents heat removal by Cu plate. This is because the heat removal at the top of the Cu plate is hot water → semi-solidified shell → Cu plate, and the heat removal at the bottom of the Cu plate is hot water → heat solidified shell → Cu plate, depending on the difference in thermal conductivity between the two. .

(I) FIG. 7 (a) shows detection from the upper side to the lower side of the continuous casting mold, in which the molten steel surface state is determined from the positive / negative sign of ΔTi (reference sign s in the figure), and The boundary position of is assumed to be an inflection position (a, b in the figure) of the positional gradient.

(Ii) Next, as shown in FIG. 7 (b), draw an approximate curve with adjacent gradient values centering on the gradient values at the inflection points a and b, and draw the peak point of the approximate curve. And feed back to the control of the level of molten steel. Note that ΔTi =
In the case of 0, the temperature distribution in the mold is measured by using the conventional method based on the distribution of Ti (θ) in the mold.

As described above, in this prior art, in brief, the change Δq in the amount of heat transfer to the continuous casting mold in the casting direction of the continuous casting mold is detected as the temperature change amount ΔTi in the sampling cycle Δθ, and ΔTi This is a technology to calculate the molten metal height from ΔL.

According to this technique, as is apparent from FIG. 8 which shows a comparison of the results obtained by measuring the actual molten metal surface level with the conventionally used immersion type gas purging type level meter,
For example, when the level of molten steel overshoots or when the level of molten steel descends and rises again, excellent accuracy of level detection is obtained.

[0017]

However, with this technique,
Due to its structure, there is a problem that a response delay occurs during the time when the Cu plate of the continuous casting mold conducts heat from the molten steel, and the response delay becomes larger as the molten metal change rate is faster. Therefore, for example, when the sliding gate of the tundish is excessively opened in the early stage of casting or when the hole diameter of the sliding gate is larger than the design value, this response delay causes the molten metal surface in the continuous casting mold to rise rapidly from the continuous casting mold. There is a possibility that the molten steel overflows.

As described above, according to the prior art, in the continuous casting process of molten metal, the molten metal level at the initial stage of casting, that is, the molten metal level in the continuous casting mold is, for example, a swirl type molten metal level that is conventionally set. It was not possible to detect the molten metal height with a high degree of accuracy and automatically control it from a time that was too low to be measured by a gauge (when the drawing speed was constant immediately after the start of drawing the continuously cast slab by the dummy bar). Of. An object of the present invention is to provide a molten metal height control apparatus and method during continuous casting that can solve the above problems.

[0019]

As a result of various studies to solve the above-mentioned problems, the inventors of the present invention have determined that the level of molten steel in the continuous casting mold is higher than that of the vortex flow type which has been conventionally installed. In addition to the molten metal level gauge 5, in the initial stage of casting, there are a plurality of sets of electrodes consisting of two conducting wires, and these electrodes are formed in a continuous casting mold with their tips separated from each other in the casting direction. The inventors have found that it is possible to solve the above-mentioned problems by installing and measuring an electrode-type molten metal level gauge arranged on the inner surface or in the vicinity thereof, and completed the present invention.

The gist of the present invention is 2
Having a plurality of sets of electrodes consisting of a book thermocouple, the electrodes are electrode type molten metal level gauges arranged on or near the inner surface of the continuous casting mold so that the tips of the electrodes are separated from each other in the casting direction. During continuous casting, characterized by having a combination with a device for adjusting the opening of the sliding nozzle of the tundish arranged above the continuous casting mold based on the signal output from the electrode type molten metal level gauge Is a molten metal height control device, when performing continuous casting of molten steel, the molten metal height in the continuous casting mold at the initial stage of casting,
By controlling using the molten metal height control device during continuous casting according to the present invention, from the initial casting of continuous casting of molten steel, the molten metal height in the continuous casting mold is detected with high accuracy and automatically. It becomes possible to control it physically.

FIG. 1 is an explanatory view showing a partially extracted structural example of a molten metal height control device for continuous casting according to the present invention. Reference numeral 1 is a continuous casting mold, reference numeral 2 is a dipping nozzle, and reference numeral is shown.
Reference numeral 11 is an electrode type molten metal level gauge, reference numerals 12a to 12d are electrodes, reference numeral 13 is an electrode fixing cover, reference numeral 14 is a float, reference numeral 15 is a dummy bar, and reference numeral 16 is a lifting hook. It is possible to measure the molten metal level below the measurable range of the level meter.

The float 14 is a distance measuring device which floats by being immersed in the unsolidified molten steel in the continuous casting mold 1 at a constant depth α, with the material, that is, the specific gravity being substantially constant (if different, corresponding by changing the material). is there.

The point of the molten metal level control device according to the present invention is that an electrode type molten metal level gauge 11 is used as shown in FIG. In other words, two conductors (thermocouple) through respective tips A electrodes 12a to 12d has a pair of spaced apart in the direction casting is _{D (A~B: l 3, B~C} : l 2, C~D:
l ₄ ) As described above, provide an appropriate potential to one of the conductors during measurement, and when the level of the molten metal reaches the tip of each electrode, the conductors conduct electricity to each other to apply the potential. The level of the molten metal is detected by utilizing the fact that the electric current flows through the conductor that was not open. The measuring range and the measuring accuracy can be freely adjusted by changing the pitch (l ₁ , l ₂ , l ₃ ) of the tip positions of the conductors and the installation position (for example, the widthwise interval between the electrodes AB).

The molten metal level gauge 11 is provided at a position where the molten steel splash from the immersion nozzle 2 does not adhere when the tundish is opened, for example, the space between the immersion nozzle 2 and the continuous casting mold 1. And, it is installed on the inner surface of the continuous casting mold or in the vicinity thereof.

In the molten metal height control apparatus according to the present invention shown in FIG. 1, the molten metal height is controlled as follows. In the figure, the distance L is the distance from the upper surface of the continuous casting mold 1 to the upper surface of the dummy bar 15, and the distance (L ₁ + α) is from the upper surface of the continuous casting mold 1 to L ₀₄ {initial setting value L ₀₄ = L- ( L ₁ +
α)}, it is possible to measure or predict the distance L and the distance α, but it is difficult to measure the distance L ₁ . Therefore, the distance L
And the distance L ₁ or L ₀₄ is determined based on the distance α. The pitches l ₁ , l ₂ and l _{3 at} the tip positions of the conductors are arbitrary and may be set as appropriate. Since the tip position A of the electrode 12a is given by _{L 04 = L- (L 1 +} α), the electrode 12b
, 12c and 12d, the tip positions B, C and D are L ₀₃ = L- (L ₁ + α) -l ₃ L ₀₂ = L- (L ₁ + α)-(l ₃ + l ₂ ) L ₀₂ = L- (L ₁ + α) - it is given by _{(l 3 + l 2 + l} 1).

Although not shown in FIG. 1, the molten metal height control apparatus according to the present invention is the same as the apparatus shown in FIG. 5 except that an electrode type molten metal level gauge 11 is added. Can be configured as. The electrode-type molten metal level gauge 11 is installed at the inner surface of the continuous casting mold 1 shown in FIG. 5 or in the vicinity thereof. For example, the tip of each electrode is 250 to 250 mm from the upper end of the continuous casting mold 1. The range is about 260 mm. That is, as shown in FIG. 5, the signal from the bath level gauge 5 is output to the microcomputer, and the signal from the electrode type bath level gauge 11 is output to the DDC 8 based on these signals. The opening signal of the sliding nozzle 7 is converted by the DDC 8.

The DDC 8 outputs an opening signal of the sliding nozzle 7 via a hydraulic servo amplifier 9 and a hydraulic servo 10. The sliding nozzle 7 is opened and closed based on this opening signal, and the flow rate of molten steel from the tundish 3 is controlled so as not to overflow from the continuous casting mold 1. Then, after the level of the molten metal of the continuous casting mold 1 rises to within the measurable range of the conventionally installed swirl type molten metal level gauge 5, for example, control by the molten metal level gauge 5 is performed. It is sufficient to automatically switch to and control the level of the molten metal.

FIG. 2 is a graph showing an example of the relationship of the sliding nozzle opening (%) at each electrode position when controlled in this way. As shown in the figure, in order to prevent the molten metal surface from rapidly rising in the continuous casting mold, the curve has a parabolic shape that is convex upward. In this way, according to the present invention, it is possible to detect the molten metal surface height in the continuous casting mold with high accuracy and automatically control it from the initial stage of continuous casting of molten steel.

[0029]

According to the present invention, the molten steel level inside the continuous casting mold is so low that it cannot be measured by a conventional eddy current level gauge, that is, the initial casting stage (in other words, the casting stage). By doing so, it becomes possible to detect the molten metal height with high accuracy from (when the drawing speed is constant immediately after the start of drawing the continuously cast slab by the dummy bar). Therefore, it is possible to eliminate the overflow of molten steel due to the time when the height of the molten metal cannot be measured.

When the molten metal level in the continuous casting mold rises to a level that cannot be measured by the electrode type molten metal level gauge used in the present invention, the molten metal level is conventionally measured. For example, since it is automatically switched to the vortex flow level meter, the level of molten metal can be measured from the initial stage of casting in continuous casting.

In the present invention, since the molten metal level in the continuous casting mold is measured by the conduction of electrodes composed of two conductors, for example, the Cu disposed on the inner circumference of the continuous casting mold is used. Compared with the method using the heat conduction of the plate, it can be performed with extremely high responsiveness.

The present invention is carried out by disposing an electrode type melt level gauge on the inner surface of the continuous casting mold or in the vicinity thereof and inputting a signal from the electrode type melt level gauge to the DDC. Therefore, the equipment modification can be suppressed to the minimum. Further, the present invention will be described in detail with reference to examples, but this is an example of the present invention and the present invention is not limited thereto.

[0033]

EXAMPLES The level of molten metal in the continuous casting mold during continuous casting was controlled by using the apparatus of the present invention having the structure shown in FIGS. 1 and 5. The electrode type molten metal level gauge 11 composed of four electrodes 12a to 12d is formed from the inner surface of the continuous casting mold 1.
It was placed in the continuous casting mold 1 separated by 3.0 mm. Distance relates to the casting direction of the distal end A to D of the respective electrodes 12a to _{12d, l 1: 50mm, l} 2: 50mm, l 3: a 50 mm, depth α: 40mm, L: was 280 mm. The casting conditions are listed below.

Steel type: [C] Ordinary steel with a content of 0.01 to 0.50% by weight Continuous casting mold width: 1240 to 2300 mm Continuous casting mold thickness: 235 mm and 300 mm, two types Number of strands: 2 Also, as a comparative example, Using the conventional device shown in FIG.
The level of the molten metal in the continuous casting mold during continuous casting was controlled under exactly the same conditions. The measured molten metal height and the amount of overshoot were continuously measured for 3 months. The amount of overshoot means the distance of (actual maximum height of the molten metal)-(target molten metal height).

The results are shown in the graph of FIG. The number of overflow occurrences per year by these two methods of controlling the level of the molten metal was calculated. The results are shown graphically in FIG.

From FIG. 3, it is understood that according to the present invention, the height of the molten metal surface, particularly the height of the molten metal surface at the initial stage of casting can be accurately measured, and the amount of overshoot leading to overflow can be greatly reduced. Further, it can be seen from FIG. 4 that according to the present invention, the overflow can be almost completely eliminated.

[0037]

As described in detail above, according to the present invention,
It is possible to accurately measure the height of the molten steel surface in the continuous casting mold from the early stage of casting, and it is possible to prevent overflow caused by the rapid rise of the molten metal surface frequently occurring in the early stage of casting.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an example of a molten metal height control device during continuous casting according to the present invention.

FIG. 2 shows each electrode position (l ₁ ,
Sliding nozzle opening at l ₂ , l ₃ and l ₄ )
It is a graph which shows an example of the relationship of (%).

FIG. 3 is a graph showing a result of an example of a conventional example and an example of the present invention.

FIG. 4 is a graph showing the results of Examples.

FIG. 5 is an explanatory diagram showing an example of the configuration of a conventional continuous casting facility.

FIG. 6 is a graph showing a correspondence relationship between the molten metal surface state (when the molten metal surface is rising, when the molten metal surface is stopped or when the molten metal surface is descending), and the positional / temporal change Δq in the amount of heat transferred to the continuous casting mold; Figure 6 (a)
6 (b) shows the case where the level is raised, FIG. 6 (b) shows the case where the level is stopped, and FIG. 6 (c) shows the case where the level is lowered.

7A and 7B are a temperature change amount ΔTi and a temperature change amount Δ for each sampling period Δθ, respectively.
Ratio of Ti to casting direction distance ΔL at sampling position ΔTi
9 is a graph showing respective values at sampling positions for / ΔL.

FIG. 8 is a graph showing a comparison of actual results of measurement of a molten metal surface level with a conventionally used immersion type gas purging level meter.

[Explanation of symbols]

1: Continuous casting mold 2: Immersion nozzle 3: Tundish 4: Continuous casting slab 5: Vortex flow level gauge 6: Installation position of device according to the present invention 7: Sliding nozzle 8: DDC 9: Hydraulic servo amplifier 10: Hydraulic servo 11: Electrode type melt level gauge 12a to 12d: Electrode 13: Conductor fixing cover 14: Float 15: Dummy bar 16: Lifting hook

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiro Araki No.3 Hikari, Kashima-cho, Kashima-cho, Kashima-gun, Ibaraki Prefecture Sumitomo Metal Industries, Ltd. Kashima Works

Claims (2)

[Claims] 1. A plurality of sets of electrodes composed of two conductors are provided,
The electrodes are output from the electrode-type molten metal level gauge, which is disposed on or near the inner surface of the continuous casting mold so that the respective tips are separated from each other in the casting direction, and are output from the electrode-type molten metal height meter. And a device for adjusting the opening of the sliding nozzle of the tundish arranged above the continuous casting mold on the basis of the signal. 2. When performing continuous casting of molten metal, the molten metal level in the continuous casting mold at the initial stage of casting is
A molten metal height control method at the time of continuous casting, which is controlled using the molten metal height control device at the time of continuous casting.