JPH02211951A - Method for continuously casting steel - Google Patents

Abstract

PURPOSE:To perfectly prevent mingle of inclusion into a mold caused by slag with a molten steel receiving part by independently and separately setting one of the molten steel receiving part through a flowing-out part, pouring part and opening device and pouring the molten steel while closing the opening device at the time of exchanging a ladle. CONSTITUTION:After detecting slag 7 at the end stage in pouring from the ladle, the pouring is stopped and the opening device 21 is closed. Even the ladle is exchanged and the molten steel is poured into the molten steel receiving part 22, the remaining slag 7 does not flow to the flowing-out part 23 in a tundish. As an air seal pipe 2 is deeply submerged into the molten steel, the remaining slag 7 is floated up and separated from the molten steel. One series of the operation after closing the opening device 21 is executed during remaining the molten steal in the pouring part 24 in the tundish. By this method, the molten steel 6 can be continuously poured into the mold 10. Therefore, as the single of the inclusion into the mold 10 caused by the slag 7 can be perfectly prevented with the molten steel receiving part 22, the cast slab having little inclusion can be stably produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for continuous casting of steel, in which while changing the ladle, molten steel is poured from the ladle into a tundish, passed through the tundish, and cast into a mold. This relates to a method for continuous casting of steel.

[Prior Art] In general, in a continuous steel casting method, molten steel in a ladle is injected into a tundish through an air seal pipe while being controlled by a sliding nozzle or a rotary nozzle, flows through the tundish, and is poured from the tundish into a sliding nozzle. It is cast into a mold through a submerged nozzle under control. Such a continuous casting method generally employs a so-called continuous casting method in which the ladle is replaced while casting. In the case of the continuous casting method, molten steel is poured from one ladle, and when the molten steel is empty, the ladle is replaced and molten steel is poured, and the molten steel is continuously poured into the mold.

In this case, at the end of pouring into the ladle, slag floating in the molten steel in the ladle flows into the tundish. This slag floats in the molten steel in the tundish and forms a slag layer. However, when replacing the ladle and starting to inject molten steel into the tundish with a new ladle, place the new ladle above the tundish, open the sliding nozzle or rotary nozzle, and inject molten steel. Lower the ladle and immerse the air seal vibrator into the molten steel of the tanditshu. Therefore, until the air seal vibe is immersed in the molten steel in the tundish, the injection flow directly floats on the molten steel in the tundish, collides with the slag layer, and drives the slag into the molten steel. This slag is injected into the mold while being mixed with the molten steel, and becomes an inclusion in the slab, causing quality defects in the slab.

Therefore, various measures have been proposed to prevent the above-mentioned slag from becoming entangled.

First, there is a means of not injecting the molten steel in the ladle until after i&, and finishing the injection of the molten steel before the slag flows out.

Secondly, a technique has been proposed in which the inside of the tundish is divided by a weir and the part into which molten steel is injected is changed for each ladle to inject molten steel. According to this technology, when pouring molten steel from a new ladle, there is no need to worry about slag getting mixed in because the molten steel receiver in the tanditshu does not contain molten steel.
Therefore, defects caused by inclusions in the slab are reduced.

Thirdly, there is a molten steel injection method as shown in FIGS. 2(a) to 2(d), which is described in Japanese Patent Application Laid-Open No. 63-177946.

(a) As shown in the figure, the cylindrical body 5 whose part is immersed in the molten steel 6 of the tundish 4 is placed at the molten metal level, and this cylindrical body 5 is
Insert the air seal vibrator into the tundish 3 to inject the molten steel from the ladle 1a, and stop the injection of molten steel 6 when the slag 7 flows out from the ladle 1a into the tundish 3, as shown in Figure (b). Remove the ladle 1a, raise the cylinder 5 as shown in FIG. and placed at the hot water level of Tanditshu 3,
The next layer ladle 1b air seal vibe is inserted into the cylindrical body 5 and molten steel is injected into the tundish.

[Problems to be Solved by the Invention] However, the above-mentioned conventional techniques each have the following problems.

The first method of leaving molten steel in the ladle reduces the yield of molten steel and is not practical. The modified method of injecting molten steel changes the installation position for each ladle, so it cannot be used with a ladle supported by a so-called swing tower, and it cannot be used when applying to an existing tundish with a small capacity. Only about two or three ladles can be replaced.

A third method of inserting an air seal vibe 2 into a cylinder 6 and injecting molten steel as shown in Japanese Patent Application Laid-Open No. 63-177946 involves raising the cylinder 5 and discharging the slag 7 inside the cylinder into a tundish 3. The process is complicated, and since some slag 7 remains, it is not possible to completely prevent the slag 7 from being rolled into the molten metal, and the slag 7 cannot be completely prevented from entering the molten metal. There is a concern about defects caused by objects.

The present invention is an attempt to solve the above-mentioned problems, and a single molten steel receiver completely prevents slag from flowing into the tundish, which occurs when changing the ladle in continuous casting, and allows continuous injection into the mold. The purpose is to provide a casting method that can be used.

[Means for Solving the Problems] The present invention provides a method for continuous casting of steel in which molten steel is poured from a ladle into a tundish, passed through the tundish, and then injected into a mold, in which the molten steel receiver of the tundish has a portion through which the molten steel flows. The molten metal receiver injects molten steel into the part from one ladle, and stops the injection after detecting the outflow of slag at the end of the injection. The switchgear is closed, the ladle is replaced, and while the molten steel remains in the injection part of the tundish, the molten metal from the replaced ladle is injected into the molten metal receiver part to float and separate the remaining slag. This is a continuous steel casting method in which the opening/closing device is then opened to allow the molten steel to flow into the flow-through portion of the tundish, and the molten steel is continuously injected into the mold.

[Operation] In the present invention, after detecting the outflow of slag from the ladle at the end of pouring, the pouring is stopped and the opening/closing device is closed. Even if the ladle is replaced and molten steel is injected into the molten steel receiver, the remaining slag will not flow into the flowing part of the tundish.
As the air seal pipe of the ladle is immersed in the molten steel, the remaining slag floats up and separates from the molten steel. A series of operations with the opening/closing device closed are performed while molten steel remains in the injection portion of the tundish, thereby making it possible to continuously inject molten steel into the mold.

[Example] The present invention will be specifically described below with reference to the accompanying drawings. FIGS. 1(a) to 1(c) are schematic diagrams showing one embodiment of the present invention.

(a) is a plan view of the present invention, in which 21 is a switchgear, 22 is a molten steel receiver, and 23 is a plan view of the present invention.
24 indicates a flow section, and 24 indicates an injection section. Here, a section 22 of the molten steel receiver is separated from a flow section 23 and an injection section 24 independently via an opening/closing device 21 on one side of the central part of the tundish 25. It is provided. Here, 26 is a refractory weir having a plurality of passage holes, and serves to rectify the molten steel and float inclusions.

(b) is a diagram showing a state in which molten steel is injected into a portion of one ladle in the present invention and continuous casting is performed.

(b) In the figure, the rotary nozzle 8 is opened from the ladle 1a and molten steel is injected into the portion 22 of the molten steel receiver via the air seal pipe 2. Since the opening/closing device 21 is open, the injected molten steel 9 flows into the flow section 23 and the injection section 24 of the tundish, and is passed through the immersion nozzle 4 while being controlled by the sliding nozzle 27 provided in the injection section 24. and then cast into the mold 10. When the molten steel in the ladle 1a is empty and it is detected that the slag 7 floating on the surface of the molten steel has flowed out into the molten steel receiver section 22, the rotary nozzle 8 is closed to stop the injection, and the rotary nozzle 8 is opened and closed. The device 21 is closed. Here, the opening/closing device 21 is composed of a guide section 31, an opening/closing plate 32, and a lifting device 33. Ladle 1a is removed and ladle 1b is installed! be done.

Section (C) is a diagram showing the state of continuous casting immediately after the ladle was replaced. (C) In the figure, the ladle 1b is installed above the molten steel receiver section 22, and then the rotary nozzle 8 is opened to inject molten steel into the molten steel receiver section 22 via the air seal pipe 2. Since the molten steel 6 and slag 7 from the ladle 1a remain in the portion 22 of the molten steel receiver, the slag 7 is driven into the molten steel 46 by the injection flow from the ladle 1b.

However, since the opening/closing device 21 is closed, the molten steel 6 mixed with the slag 7 does not flow out to the reflux section 23 and injection section 24 of the tundish, and the molten steel surface in the molten steel receiver section 22 gradually rises. The slag discharge port 34 is reached. During this time, the air seal pipe 2 is immersed in the molten steel, and the slag 7 and the molten steel mixed with the slag float up and separate from the molten steel 6, and are discharged from the slag discharge port. At this stage, the opening/closing device 21 is opened, and the molten steel receiver flows out the molten steel in the section 22 to the reflux section 23 and the injection section 24 of the tundish. and molten steel 6
is a sliding nozzle 27 provided in the injection part 24
The liquid is cast into the mold 10 through the immersion nozzle 4 while being controlled by the immersion nozzle 4 and the like. A series of operations after closing the opening/closing device 21 are performed while molten steel remains in the injection portion of the tundish, thereby making it possible to continuously inject molten steel into the mold. The molten steel 6 poured into the mold 10 is pulled out by pinch rolls (not shown). Two are unsolidified parts 30
It is a slab with

Next, an experimental example in which the method of the present invention was carried out using the apparatus shown in FIG. 1 will be explained.

(Experiment example) Table 1 shows the results of casting slabs of low-Al quilted steel with a shoulder thickness of 250 m and a width of 10,001 cm. The evaluation was performed using the total oxygen amount: T(0). A comparison was also made with a conventional example that does not use the method of the invention.

Table 1 T(0) Unit: (ppm) As is clear from Table 1, similar values of T(0) were obtained in the method of the present invention regardless of whether the ladle was replaced.

On the other hand, the conventional method had a higher value than the method of the present invention, and the value also showed a tendency to increase as the number of charges increased.

As an embodiment of the method of the present invention, the molten steel receiving portion 22 is provided on one side of the central portion of the tundish 25 and is independently separated from the flow portion 23 and the injection portion 24 via a closure 221. However, the present invention is not limited to this, and if the capacity of the tundish is large, it may be provided within the tundish. However, in any case, one molten steel receiver can flow through the portion 22 independently. Part 23
, it is necessary to provide it separately from the injection part 24. This eliminates unnecessary parts of the equipment, fixes the installation position of the ladle to be replaced, and facilitates operation.

In the method of the present invention, when replacing the ladle, the molten steel receiver can be automatically operated by connecting the detection of slag flowing out to a portion, the floating separation of the remaining slag, and the opening and closing of the opening/closing device.

[Effects of the Invention] According to the method of the present invention, one molten steel receiver is provided with a flow passage portion, a pouring portion, and a switching device independently separated from each other, and when replacing the ladle, the opening and closing device is closed to prevent pouring. Through the simple operation, the molten steel receiver can completely prevent inclusions caused by slag from entering the mold, so slabs with low inclusions can be stably produced.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an injection device using a cylinder of a conventional continuous casting method. 21... Switchgear, 22... Molten steel receiver is part, 23...
...Flowing part, 24...Injection part, 25...Tandish.

Claims (1)

[Claims] In a continuous steel casting method in which molten steel is injected from a ladle into a tundish, passed through the tundish, and injected into a mold, the molten steel receiving part of the tundish is connected to a passing part and an injection part through a switching device. It is installed separately and molten steel is poured into the molten steel receiving part from one ladle.
After detecting the outflow of slag at the end of the injection, stop the injection, close the opening/closing device, replace the ladle, and remove the molten steel from the replaced ladle while the molten steel remains in the injection part of the tundish. The molten steel is injected into the molten steel receiving part, the remaining slag is floated and separated, and then the opening/closing device is opened to flow the molten steel into the flow part of the tundish, and the molten steel is continuously injected into the mold. Continuous casting method for steel.