KR950005279Y1 - Flow control tundish - Google Patents

Abstract

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Description

Flow control small tundish

1 is a schematic diagram of a conventional tundish in which weirs and dams are installed.

2 is a schematic diagram of a conventional tundish capable of flow control by an electromagnetic field.

3 is a schematic diagram of an experimental apparatus used to detect the RTD effect by gas blowing.

4: RTD curve without flow control in rectangular container.

5: Optimal RTD Curve with Flow Control by Gas Blowing in Rectangular Containers.

Figure 6: Schematic diagram of a conventional tundish for long width twin roll stripcasting.

7 is a partial cross-sectional schematic view of a tundish in accordance with the present invention.

8 is a plan view of a tundish according to the present invention.

* Explanation of symbols for main parts of the drawings

41: Upper Lance 42: Lower Nozzle

61: inert gas supply source 62,63: inert gas supply line

The present invention relates to a tundish positioned between a ladle and a casting apparatus as a medium for supplying molten steel to a casting process, and more particularly, to a small tundish capable of flow control by inert gas blowing.

Tundish not only serves to smoothly supply uniform molten steel to the casting site, but also functions as a final refining device to filter out impurities such as non-metallic inclusions, which is an important problem directly related to the quality of cast products. Therefore, the flow of molten steel in the tundish must be designed to be suitable for performing these functions, which is closely related to the shape and operating parameters of the tundish. Especially in strip casting and electromagnetic casting (EMC), the capacity of the tundish is small and the bath height is shallow so that the molten steel can be pulled out in a very short time, sometimes requiring special shaped tundish. Therefore, in the tundish applied to such a casting process, the importance of flow control is particularly important. In other words, while the average residence time of 30-40 tons of tundish used for playing large slabs is about 10 minutes, the tundish is used in the strip casting process of casting strips of width 1100 mm and thickness 2 mm at a speed of 120 m / min. Since the capacity of is about 1-2 tons, the average residence time of the molten steel in the tundish is only about 1 minute. Thus, without fine flow control, the molten steel exits directly to the outlet before it is even mixed and stirred.

In general, if the flow rate Q of the molten steel is determined by the casting speed at which the capacity V of the tundish is determined, the average residence time in the tundish is determined as V / Q, but the residence time of the molten steel is determined by the mixed state in the tundish. Has a distribution. The most important factor in determining the flow state in tundish is the residence time distribution (RTD), which is a measure of the distribution of time that molten steel entering the ladle simultaneously exits the tundish. It may be indirectly determined whether it has been homogenized and sufficient time has been provided to float out the impurities. In other words, the flow in the tundish should be directed so that the peak of the RTD curve is near the mean residence time and as close as possible to the flow of plugs, that is, the molten steel, which flows side by side instead of only one part. The stagnant region in the vessel should be removed to achieve homogenization of temperature and composition, which can be easily seen through the interpretation of the RTD curve. In other words, the increase in the plug fraction is directly related to increasing the reaction rate between slag / metal in the vessel, thereby determining whether the fluid element in the vessel has evenly exited the outlet after experiencing the flotation separation time of the inclusions. Because it can.

Attempts have been made to obtain suitable RTD curves, representative examples of which are shown in FIGS. 1 and 2.

1 is a tundish provided with a physical shield such as a weir 13 and a dam 14 between the molten metal inlet 11 and the molten metal outlet 12 opened and closed by the stopper 15. 10), FIG. 2 shows a tundish in which electromagnetic field imparting means 23 are formed at specific portions between the inlet 21 and the outlet 22 to induce plugs by applying a strong magnetostatic field. (20) is shown.

However, in the case of controlling the flow by installing the ware 13 and the dam 14 as shown in FIG. 1, not only the high temperature wear resistant refractory material is additionally required but also another stagnant zone is formed at the position immediately after the shielding to improve efficiency. There are problems such as dropping and mixing of large inclusions of abrasive impurities.

In addition, the method of controlling the flow by the magnetic field as shown in FIG. 2 has been proposed theoretically in terms of the effect, and has not yet been practically used because it requires additional expensive equipment.

Recently, a technique for blowing inert gas such as argon has been proposed in tundish operation, which is mainly used in large tundish or in a tundish with a relatively long residence time to reduce congestion area. It is aimed at the same primary effect.

However, this technique has a problem in that it is not possible to properly modify the distribution of residence time in a small tundish operation having a very short residence time.

The present invention effectively controls the internal flow occurring in a short time by installing the upper lance at the top to blow inert gas by the impact jet and / or installing the lower nozzle at the bottom to blow the inert gas. The present invention aims to provide a small, controllable tundish that can be used.

Hereinafter, the present invention will be described.

In general, top and bottom blowing or combined blowing are performed on a continuous flowing rectangular reaction vessel to investigate the distribution of residence time of the RTD peak. In addition, there has been a report that the plug flow fraction has been improved due to the decrease of the congestion zone. [Ph. D thesis: J. H. Zong, Seoul National University (1988) J. H. Zong, J. K. Yoon: Submitted to Metal Trans, B, (1991)]

According to the experimental results of the present inventors, this results in the formation of a local mixing cell by gas blowing, whereby the fluid is temporarily trapped in the mixing zone, stirred and exited, and the fluid as a whole is plugged. It was found that a small amount of odor through the bottom nozzle at the bottom was very effective in removing the congestion zone.

On the other hand, a method of effectively analyzing the RTD curves experimentally obtained through a hand model experiment and a method of deriving suitable blowing conditions are presented.

3 is a schematic diagram of the experimental apparatus used for the RTD measurement in the preliminary experiment, in which water with a controlled quantity is injected into a rectangular (100 × 30 × 60 cm 3) acrylic container 1 through a water container 2. At the same time, various types of gas blowing are performed through the upper lance 4 and the low odor nozzle 5 from above the vessel 1.

At this time, a skimmer 3 was installed to suppress the ripple effect of the injection inertial force and to investigate only the flow control phenomenon caused by the injection of pure gas, and a platinum electrode 7 was installed at the outlet of the vessel to detect the RTD signal. . When a KN solution of 2N concentration is injected at the inlet at a moment, the conductivity of the KCI solution is measured by the conductivity measuring device 7a through the platinum electrode 7, and the exit signal is detected by the difference in electrical conductivity. Through the A / D converter 7b, it is converted into a digital signal and stored in the computer 7c.

In Fig. 3, reference numeral 6 denotes a valve. In this case, the present inventors statistically integrate the RTD curve obtained in the experiment, and the dimensionless average residence time When the dispersion value is obtained, the plugs can be calculated by It turns out that I can express properly.

The present inventors conducted a male model experiment using the experimental apparatus shown in FIG. 3 to investigate the effect of gas blowing on the plugs, and the results are shown in FIGS. 4 and 5.

The experimental method is as follows. That is, the water of which the quantity is controlled is injected into the acryl container 1 of the rectangular shape (100 × 30 × 60 cm), and at the same time, the inert gas stored in the gas container 8 through the central lance L ₃ of the upper lance 4. Is measured with a flow meter (8c) and blown over the vessel (1) at a flow rate of 90 (l / min) and 30 (l / min) at each of the three upper lances (L ₁ , L ₂ , L ₃ ) on the inlet side. Flow rate of the nozzle and the RTD curve at the time of auxiliary blowing of 1 (l / min) through the B ₅ nozzle of the low blowing nozzle (5), and as a result and the plug fraction obtained by the above formula (1) Are shown in Figures 5a and 5b, respectively.

At this time, the height of the water surface was 10cm, the height of the upper lance 4 was 2cm above the water surface, the diameter of the upper lance 4 was 2.8mm, the cavity depth was about 30% of the total bath.

4 is the RTD curve when there is no flow control by gas blowing and the plug fraction obtained by the above equation (1). Indicates.

As shown in FIG. 4 and FIG. 5, the plug fraction when there is no gas blowing (FIG. 4) Is 0.092, whereas in case of gas blowing using a single lance, the plugs fraction is shown in FIG. Is 0.267 and three lances are installed in series along the direction of fluid flow and nozzles are installed in the stagnation zone. In Fig. 5b, the plug fraction is 0.434, and gas is blown in accordance with Fig. 5b. It can be seen that the plug fraction is increased by 4 times compared to the case where no gas blowing is performed.

On the other hand, even if additional dams were physically installed in this complex blow method, there was no difference in plug flow rate, which proves that the gas blowing method far exceeds the dam's effect. Considering the adverse effects such as the formation of stagnant zones caused by the installation of dams, the increase of expenses, or the incorporation of abrasive impurities, flow control by gas injection has a rather superior alternative effect.

The above results are summarized as follows.

That is, a), the blowing of gas by the upper lance in the continuously flowing reaction vessel is very effective in improving the plug fraction, and b), in case of blowing the gas at the same flow rate, (A) The effect of lower swelling by the lower nozzle in the area where the congestion area is expected would result in an additional increase in the fraction of plugs due to the reduction of the congestion area. However, the flow condition of the lance may vary depending on the lance size and height, but the depth of impact jet penetration can be maximized at the level of 30-40% of the total bath. It can have the adverse effect of reduction and scattering and physical damage of the floor, and e) it is simpler than the flow control method by installation of physical dam. There is an equivalent substitution effect.

Hereinafter, the present invention will be described.

The present invention is formed in a small tundish which is formed in the upper portion of the melt inlet for introducing the molten metal to the inside, and the melt discharge portion for supplying the internal melt 110 to the casting device 50 therein A one or a plurality of top lances connected to a source of inert gas are installed thereon between the molten metal inlet and the molten metal outlet; In addition, the present invention relates to a small tundish configured to allow flow control by forming one or a plurality of low odor nozzles connected to a source of an inert gas in a molten metal anticipated region where stagnant melt is expected.

Hereinafter, the present invention will be described in detail by the drawings.

As a tundish to which the present invention can be applied, a tundish for the long width twin roll strip casting shown in FIG. 6 is provided. As shown in FIG. 6, the tundish 30 has a capacity inside. A molten metal inflow portion 31 for flowing in is installed at an upper portion thereof, and a molten metal discharge portion 32 for supplying an internal molten metal to the casting apparatus 50 is formed at the lower portion thereof. In Fig. 6, reference numeral 33 denotes a tundish stopper.

In order to cast the long strip 112 using the tundish 30, the roll of the casting device 50 in which the side dam 52 is constructed from the tundish 30 through the melt discharge part 32 ( 51) Since the slits need to be distributed as long as possible to the site, the shape of the tundish is preferably a trapezoidal spread tundish rather than a general rectangular tundish, so that the molten portion of the tundish is discharged. A long elongated slit-type nozzle is used as 32.

Therefore, in the tundish for the long width twin roll strip casting, non-uniform flow such as the molten steel stagnation zone and bypass is generated and more likely to be mixed between the rolls 51, and the melt inlet portion 31 in the tundish. ) And the distance between the molten metal discharge part 32 is very short, it becomes more important to make the flow into the plugs, the invention can be applied more effectively to this tundish.

As shown in FIG. The tundish 100 of the present invention includes one or a plurality of upper lances 41 installed between the melt inlet 31 and the melt discharge 32; And one or a plurality of low odor nozzles 42 formed in the molten metal expected region.

The upper lance 41 is connected to the inert gas supply device 60 in a gas through relationship, the inert gas supply device 60 is an inert gas supply 61 for storing the inert gas, and the inert gas supply source ( 61 and a first inert gas supply line 62 for connecting the upper lance 41 in a gas through relationship, the inert gas supply line 62 is provided with a pressure gauge 62a and a flow meter 62b. have.

The upper lance 41 may be any conventional lance capable of blowing gas, and the number, position, and arrangement of the upper lance 41 may vary depending on the size and shape of the tundish.

The gas blowing flow rate through the upper lance 41 is determined by the lance diameter and height, and the gas blowing to form a depth of about 30-40% of the bath height under the condition that no splashing of molten steel occurs. It is desirable to determine the flow rate.

The low odor nozzle 42 has a form of a conventional nozzle or a porous plug, and is configured to homogenize the molten metal by distributing one or more portions at a site where capacity retention is expected.

An example of a tundish to which the present invention is applied is shown in FIG. 8, and in FIG. 8, a low odor nozzle 42 is formed at a portion facing the melt inlet 31 based on the melt discharge unit 32. have.

The low odor nozzle 62 is also connected to the inert gas supply source 61 by a second inert gas supply line 63 in a gas through relationship. The first inert gas supply line 63 is also provided with a pressure gauge 63a and a flow meter 63b.

In order to reduce the cooling of the molten metal by blowing the gas supplied through the upper lance 41 and the low odor nozzle 42, the inert gas is fixed before blowing the inert gas through the upper lance 41 and the low odor nozzle 42. It is preferable to install heaters 64 configured to heat the temperature in the first and second inert gas supply lines 62 and 63.

The upper nozzle 41 and the lower nozzle 42 may be connected to the same inert gas source or a separate inert gas source as shown in FIG.

In addition, the heater 64 may also be installed to supply the heated inert gas to the first and second inert gas supply lines 62 and 63 at the same time or may be installed in each supply line to supply separately. .

According to the present invention, the inert gas such as argon gas is blown to form a cavity by an impinging jet through the upper lance 41 properly distributed immediately after the tundish injection. The part which is easy to generate | occur | produces the flow of a plug by blowing a small amount of inert gas through the low odor nozzle 42.

The present invention is not limited to the tundish for long-width twin roll strip casting shown in FIGS. 7 and 8, but is applicable to any tundish where it becomes important to form the flow into plugs.

In the present invention, it is preferable to make the inert gas atmosphere by appropriately using the tundish cover, so that the reoxidation is prevented as much as possible to prevent the incorporation of the oxide into the mold.

As described above, the present invention can bring the following effects by plugging the flow and removing stagnant zones through appropriate inert gas blowing in a small capacity special type tundish operation such as strip casting or electromagnetic casting.

First, the inlet gas is divided and blown in the direction of flow through the upstream lance, thereby increasing the plug fraction by the effect of the tank-in series.In the lower part of the cavity, a flow field with an upward flow is formed, resulting in the occurrence of inclusions. Promote separation.

Second, the low odor nozzle blows a small amount of inert gas into the anticipated stagnation zone, thereby improving the overall plug fraction.

Third, by using a heater and a tundish cover of the inert gas, it is possible to operate in the maximum inert gas atmosphere and to prevent the reoxidation of clean steel.

Fourth, the blowing of inert gas is more advantageous in the manufacture of clean steel because impurity residues are also adsorbed on the gas bubbles and floated.

Fifth, by the complex blowing method as described above, it is possible to bring about an alternative effect on expensive methods such as the installation of a dam or the use of a static magnetic field to increase the plug fraction.

Claims (1)

A molten metal inflow portion 31 for injecting the molten metal 110 into the upper portion is formed therein, and a molten metal flow portion 32 for supplying the molten metal 110 to the casting device 50 is located therein. In the small tundish formed at the one or more upper lances 41 connected to the source 61 of the inert gas, the upper portion is disposed between the molten metal inlet 31 and the molten metal outlet 32. One or more low-nozzle nozzles 42 connected to the source 61 of inert gas are formed on the molten metal anticipated portion and configured to enable flow control.