JPH0620628B2 - Residual hot water level detection device in tundish and continuous casting control method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to detection of a residual hot water level in a tundish in continuous casting and a casting control direction using the same, and particularly, although not intended to be limited to this, in a pan. The present invention relates to a residual hot water level detection device suitable for continuous casting of different steel types, which is performed by continuously casting different types of molten steel in a subsequent ladle, and a casting control method using the same.

[Conventional technology]

Continuous casting of different steel grades using the same tundish has been carried out constantly for the purpose of improving productivity and reducing the cost of tundish refractories.

As a conventional method for successively casting different steel types using the same tundish, for example, after completely injecting the molten steel in the pan from the tundish into the mold, the withdrawal of the slab is temporarily stopped and the molten steel in the subsequent pan is melted. After starting pouring into the tundish to reach a certain level of the molten metal surface, pouring into the mold is restarted and continuous casting is performed.

Alternatively, after injecting the molten steel in the pan from the tundish into the mold, raise the tundish (in some cases, further traverse) and after pumping out and removing the tundish slag and mold powder that have flowed into the mold, If necessary, insert an iron plate to prevent mixing of molten metal on the surface of the molten metal, set the tundish again in the mold, start pouring molten steel in the rear pan into the tundish, and perform continuous casting. 63-174769).

In the conventional continuous casting method of different steel types, a method of visually recognizing the outflow of the slag in the tundish into the mold that the molten steel in the pan has completely disappeared from the tundish is used. However, there is a problem that a large amount of slag in the tundish flows out into the mold, and it takes a long time to remove it, which deteriorates productivity, and the solidified shell shrinks, causing breakouts from the cast seam portion one after another. There is a problem to do.

To avoid this problem, measure the amount of residual molten steel in the tundish with a weighing machine such as a load cell or a measuring rod, and when the target small amount of residual molten steel is reached, start injecting the molten steel in the rear pan. There is a method in which molten steels in the front and rear pans are mixed in a tundish to perform continuous casting of different steel types (JP-A-62-148).
066, JP-A-63-80947).

However, since the measurement accuracy of the residual molten steel amount is low in these methods, the mixed amount of the molten steel in the front ladle and the latter ladle varies in the tundish, resulting in a slab ( In the following, there is a drawback that the length of the seam piece varies, and in terms of quality assurance, the seam piece has to be cut off for a long time in consideration of the margin, resulting in a problem that the yield of the first grade product decreases. there were.

[Problems to be Solved by the Invention]

In successive castings of different steel types in the same tundish, the molten steel in the front ladle and the molten steel in the rear ladle mix in the tundish. It may not be included in the composition range of either molten steel of the ladle or the ladle, and the component distribution of the joint piece gradually changes between the components of the ladle and the ladle, so it cannot be counted as a first-class product. . For this reason, there is a problem that this joint piece must be cut out and scrapped.

In the conventional method of measuring the amount of residual hot water in a tundish using a weighing machine such as a load cell or a measuring rod, there is a large weighing error.
Since the length of the seam piece easily changes due to casting,
In the actual operation, the joint piece had to be cut and removed for a long time. In order to solve this problem, the problem is to adjust the amount of residual hot water in the tundish of the pan to be as small as possible and with high reproducibility.

[Means for Solving the Problems]

Residual hot water level detector for tundish of the present invention (12-18)
Is the electrode A exposed to the molten steel side through the tundish (1) from the bottom of the tundish (1) or the wall surface near the bottom.
(12, 13), the electric wiring (15) connected to the mold (9) or a portion that is electrically connected to the mold, and an increase in electric resistance between the electrode A (12, 13) and the electric wiring (15). Detection device to detect (17,
18). In addition, the symbols given to the corresponding elements in the examples described later are shown in parentheses for reference.

In one embodiment of the present invention, the detection device (12-18) comprises a power source (16) for applying a constant voltage between the electrode A (12, 13) and the electric wiring (15), and the electrode A (12). , 13) and the electric wiring (15), the current detection means (17) for detecting the level of the current flowing, and a means for detecting a decrease in the current level detected by the current detection means (17) above a predetermined level. (18), inclusive.

In one usage mode of the detection device (12-18), the electrode A (12, 1
3) is installed at a plurality of positions in the vertical direction and the extraction speed is reduced in response to the increase in the electric resistance between the upper electrode A and the electric wiring (15) to lower the lower electrode A and the electric wiring (15). The stopper is fully closed in response to the increase in electric resistance during the period, and the casting is completed.

In one usage mode in continuous casting, using the same tundish, when performing continuous casting of different steel types with different molten steel components, when the detection device detects an increase in electrical resistance,
While the casting of the residual molten steel in the tundish poured from the first pan is continued, the injection of the molten steel in the second pan into the tundish is started.

In another usage mode in continuous casting, when performing continuous casting of different steel types having different molten steel components using the same tundish, the tundish nozzle is temporarily closed when the detection device detects an increase in electric resistance. At the same time, the withdrawal of the slab is temporarily stopped, then the injection of the molten steel in the subsequent pan into the tundish is started, and the injection into the mold and the withdrawal of the slab are restarted when the predetermined molten metal surface height is reached.

Hereinafter, these contents will be described with reference to the drawings.

Figure 1a shows the tundish (hereinafter referred to as TD) and T
The structure of the residual hot water level detection device in D is shown. 1 is TD iron skin,
2 is a TD lined refractory material, 3 is a stopper, 4 is a stopper support arm, 5 is a stopper drive device, 6 is molten steel in TD, 7 is slag in TD, 8 is a dipping nozzle, 9 is a mold, 10 is a cast piece, 11 Is a pinch roll, 12 and 13
Is an electrode A embedded in a refractory and having its tip exposed from the TD wall and contacting molten steel. A plurality of electrodes A may be provided in the vertical direction so that the difference in molten steel level can be detected.

14 is an electric wiring connected to the electrode A, 15 is a mold (or a dipping nozzle in conduction with the mold, TD iron skin or TD)
(E.g., car), 16 is a battery, 17 is an ammeter, and 18 is a current change rate calculation device. Note that 17 may be an ohmmeter that measures the resistance value between the electrode A / electrical wiring 15, and 18 may be a resistance value change rate calculation device.

Here, the mold 9 has a function as another electrode (earth electrode) for detecting whether or not molten steel is present in the electrode A portion. Hereinafter, this is referred to as an electrode B.

The principle of detecting the residual hot water in the TD will be described below. When molten steel is present in the TD and the electrode A is in contact with the molten steel, the electrode A 12, the molten steel 6, the immersion nozzle 8, the mold 9 (electrode B), the electric wiring 15, the ammeter 17, the battery 16 and the electricity are used. An equivalent circuit of the electric circuit constituted by the wiring 14 is shown in FIG. 1b. A current given by the following equation flows in this electric circuit.

I = E (R + Rs) (1) where I is the current (A) flowing in the electric circuit, E is the applied voltage (V), Rs is the electric resistance (Ω) of molten steel or slag, and R is other Is the electrical resistance of. When a voltage of several volts is applied to the battery, the electric resistance is small and a relatively large current flows because molten steel exists in the TD. But,
When the amount of residual hot water in the TD decreases and the slag in the TD contacts the electrode A, the electrical resistance increases and the current decreases. The reason for this is
This is because the specific resistance of the slag in the TD containing Al ₂ O ₃ , SiO ₂ , MgO, CaO, etc. is significantly larger than the specific resistance of the molten steel.

FIG. 2 shows an example of current change measured by the inventors. In FIG. 2, when the molten steel of the pan is in the TD, a high current flows in the electric circuit of the residual hot water level detection device in the TD because the electrode A is in contact with the molten steel of the pan. There is. However, when the pouring of the pan is completed and the molten steel surface in the TD is lowered, the molten steel falls below the level of the electrode A, and the slag contacts the electrode A, the current value sharply drops. When the slag drops below the electrode A, the current value further decreases. FIG. 2 shows that the injection of the rear ladle then starts and the molten steel surface in the TD rises, and the current value sharply rises when the electrode A starts to contact the molten steel in the rear ladle. Since the electrode A is embedded in a refractory lining in a high temperature and oxidizing atmosphere for a long time, it is important that it is made of a material having excellent heat resistance and oxidation resistance.

Next, a continuous casting method for different steel types using the above-mentioned TD residual level detecting device will be described.

In the first mode (method A), the device configuration shown in FIG. 3 is adopted. That is, the current change rate calculation device 18 uses the current change rate ΔI.
/ In (In is the current value when molten steel is in constant contact with the electrode A, ΔI is the amount of decrease from In), and when a rate of change above a certain level is detected, the ladle nozzle drive control device 19 In addition, an operation command is output to the alarm device 20, and the molten steel injection in the rear pan is started while continuing the casting of the residual molten steel in the TD injected from the front pan.

Further, in the second mode (method B), when the device configuration shown in FIG. 4 is adopted and the current change rate computing device 18 detects a current change rate higher than a certain level, the stopper drive control device 21,
An operation command is output to the pinch roll drive control device 22 and the alarm device 20, the stopper 3 is once closed, the withdrawal of the slab is temporarily stopped, then the molten steel injection in the rear ladle is started, and the predetermined molten metal height is reached. At that point, injection into the mold and withdrawal of the slab are restarted.

In FIGS. 3 and 4, the alarm device 20 is for notifying the operator of the detection of the residual hot water in the TD (no contact with residual hot water), and uses a siren or a buzzer etc. In each of the casting methods (method A and method B), the amount of residual hot water in the TD can be grasped in a small amount and with high accuracy as compared with the conventional continuous casting method of different steel types, so that the length of the joint piece can be shortened. In addition, method A has the advantage that the work is simple, while method B does not allow the ladle nozzle to spontaneously open (starting the injection with a single nozzle opening operation) at the start of the injection of the ladle, so that the injection of the ladle can be started. Even if it is delayed, there is an advantage that continuous casting is possible.

Although the above description has been described as being particularly effective in continuous casting of different steel types, it goes without saying that the effects of the present invention can be enjoyed also in continuous casting of the same steel type.

[Action]

According to the present invention, the TD residual hot water level detection device has a simple structure, and a predetermined amount of residual hot water is accurately detected. With continuous casting using this, the variation in the length of the joint piece is reduced, the length of the joint piece to be cut off is shortened, and the yield of the continuous casting is improved.

〔Example〕

Examples will be described below. Heat size 160 T / Ch
Carbon steel for machine structure is smelted in the converter of
A curved continuous casting machine was used to cast a slab with a cross-sectional size of 170 mm × 170 mm. Molten steel of the front ladle was S45C, molten steel of the rear ladle was S10C, and different steel grades were continuously cast with a TD of 30 tons capacity equipped with the residual hot water level detection device in the TD shown in Fig. 1a.

As the electrode A, a high chromium stainless steel wire (3 mmφ) having excellent heat resistance and oxidation resistance was embedded in a TD lined refractory and exposed from the side surface close to the TD lower part to the molten steel side. The position of the molten steel contact end of the electrode A was adjusted in advance so that the amount of TD remaining hot water when detecting that there was no residual hot water contact was 3 tons. On the other hand, as the battery 16, a 1.5-volt DC battery was used.

S45C of the first pan was cast at a casting speed of 2.5 m / min, and after pouring the ladle, the rear pan was placed on the ladle turret to complete the preparation for pouring.

Successive casting operations of different steel types (method A) shown in FIG. 3 were performed. That is, the amount of remaining hot water in the pan is reduced, and the current change rate calculating device of the remaining hot water detecting device in the TD changes the current more than a certain amount (in this case, 50%
(Decreases below), the ladle nozzle drive control device 1
9 and the alarm device 20 to output an operation command to open the nozzle,
S10C in the rear pot was started to be injected, and different steel types were continuously cast.

Next, the same steel type was used to successively cast different steel types shown in FIG. 4 (method B). That is, when the rate of change in current dropped to 50% or less, an operation command was output to the stopper drive control device 21, the pinch roll drive control device 22 and the alarm device 20, and the stopper 7 was once stopped. Next, the molten steel injection in the rear pan was started, and when the amount of molten steel in the TD reached 15 tons, the injection into the mold 2 and the withdrawal of the cast slab were restarted.

The lengths of joint pieces (portions that cannot be applied to S45C or S10C) obtained by these methods are shown in FIG. 5 together with comparative examples. In FIG. 5, n is the number of samples, X is the average value of the seam piece length, and σ is the standard deviation.

In the comparative example, the target amount of TD remaining hot water in the pan is set to 3 tons, and different steel grades are cast continuously using the measured load cell value. However, due to the effect of TD ingot and measurement error of the load cell, the joint piece length There is a large variation in On the other hand, in the examples of the present invention (method A and method B),
The seam piece length is clearly shorter and more stable than the comparative example.

〔The invention's effect〕

In the present invention, since the amount of residual hot water in the TD can be accurately grasped, it is effective in reducing the seam piece length in continuous casting of different steel types (improvement of casting yield), and the slag in the TD flows out into the mold. Can be reliably prevented, which is effective in stabilizing the operation. Further, since the measurement with the conventional measuring rod can be omitted, the load of the continuous casting work can be reduced, and its application effect is extremely large.

[Brief description of drawings]

FIG. 1a is a block diagram showing the structure of the residual hot water level detection device in the TD according to the present invention, FIG. 1b is an equivalent electric circuit diagram of the residual hot water level detection circuit in FIG. 1a, and FIG. 2 is the residual hot water level in the TD. It is a graph which shows the example of the electric current change measured with the detection apparatus. 3 and 4 are block diagrams showing one embodiment of the present invention, respectively, and FIG. 5 is a graph showing the results of continuous casting of the embodiment shown in FIGS. 3 and 4. 1: TD iron skin, 2: TD refractory lining 3: stopper, 4: stopper support arm 5: stopper drive device, 6: TD molten steel, 7: TD inner slag, 8: dipping nozzle 9: mold, 10: cast slab 11: Pinch roll, 12: Electrode A 13: Electrode A, 14: Electric wiring 15: Electric wiring, 16: Battery 17: Ammeter, 18: Current change rate calculation device 19: Ladle nozzle drive control device, 20: Alarm Device 21: Stopper drive control device 22: Pinch roll drive control device, 23: Ladle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Narita Tsu, 12 Nakamachi, Muroran City, Hokkaido Stock of Nippon Steel Co., Ltd. Inside the Muroran Ironworks

Claims (5)

[Claims] 1. An electrode A exposed through a tundish from a bottom portion or a wall surface near the bottom portion to the molten steel side, an electric wiring connected to a mold or a portion electrically connected to the mold, the electrode A and an electric wiring. The residual hot water level detection device in the tundish, which comprises a detection device for detecting an increase in electrical resistance between the two. 2. A detection device, a power supply for applying a constant voltage between the electrode A and the electric wiring, a current detection means for detecting a level of a current flowing between the electrode A and the electric wiring, and A means for detecting a predetermined or more decrease in the current level detected by the current detecting means, the claim 1
The residual hot water level detection device in the tundish according to the item (1). 3. A plurality of electrodes A having different vertical positions exposed through a tundish from a bottom portion or a wall surface near the bottom portion to the molten steel side, and an electric wiring connected to a mold or a portion electrically connected to the mold. , The withdrawal speed corresponding to the detection of the increase in the electric resistance of the upper electrode of the residual hot water level detection device in the tundish, which is composed of a detection device for detecting the increase in the electric resistance between the electrode A and the electric wiring. A continuous casting control method in which the stopper is fully closed in response to the detection of an increase in the electric resistance of the lower electrode by deceleration. 4. When continuously casting different steel types having different molten steel components using the same tundish, the electrode A exposed through the tundish to the molten steel side from the bottom of the tundish or a wall surface near the bottom and the mold or For detecting an increase in electric resistance of a residual hot water level detecting device in a tundish, which includes an electric wire connected to a portion electrically connected to the mold and a detecting device for detecting an increase in electric resistance between the electrode A and the electric wire. Correspondingly, the continuous casting control method is to start casting the molten steel in the rear pan into the tundish while continuing to cast the residual molten steel in the tundish injected from the first pan. 5. When performing continuous casting of different steel types having different molten steel components using the same tundish, the electrode A exposed from the bottom of the tundish or the wall surface near the bottom to the molten steel through the tundish, the mold or For detecting an increase in electric resistance of a residual hot water level detecting device in a tundish, which includes an electric wire connected to a portion electrically connected to the mold and a detecting device for detecting an increase in electric resistance between the electrode A and the electric wire. Correspondingly, once the tundish nozzle is closed and the withdrawal of the slab is temporarily stopped, then the pouring of the ladle molten steel into the tundish is started, and when it reaches the predetermined molten metal level, it is injected into the mold. Restart drawing of the slab,
Continuous casting control method.