JPS63238962A - Tundish for continuous casting - Google Patents

Abstract

PURPOSE:To reduce inclusion in a cast slab by arranging a covering body having airtightness closing an inner part in casting start tube of a tundish and cutting off invasion of outer air into main body. CONSTITUTION:The covering body 5 having airtightness, is inserted at position having the prescribed height in the casting start tube 2 arranged discharging hole 6 in the tundish 1. The covering body 5 composing of flat disk plate, is brought into closely contact with the inner face of the tube at the intermediate position of the tube 3 and the inner part in the tundish 1 is cut off from outer air and also the covering body 5 disappears at the stage of flowing the molten metal into the inner part 4, and after that, the molten metal flow is not disturbed. At the time of casting the molten metal through the tundish 1, as the tundish 1 is perfectly sealed, and held to reducing atmosphere, the inclusion composing of oxide in the cast slab is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tundish for continuous casting equipped with a sliding nozzle, and more particularly to means for making the atmosphere inside the tundish reducible at the start of casting.

[Prior Art] As shown in Fig. 5, the pouring port of a continuous casting tundish equipped with a sliding nozzle is connected to a discharge port 6 penetrating the bottom of the main body 1 of the tundish, and a casting nozzle 7 mounted below the discharge port 6. The casting nozzle 7 consists of a sliding nozzle 8 and an immersion nozzle 9. Further, a casting start pipe 2a (see FIG. 6) is generally attached to the discharge port 6.

The sliding nozzle 8 is a device that shuts off the WI field flow or adjusts the 1M by attaching a drinking cutoff plate below the discharge port 6 and sliding the plate.

The immersion nozzle 9 is a device for protecting the surface of the molten metal flowing down the discharge port 6 from the outside air, and as shown in FIG. By covering it with the powder 12, there is an effect of completely shielding the Wl bucket 10 from the outside air. Therefore, during casting, as long as each hole 16, 17 in the ceiling 15 of the tundish 1 is completely sealed, WJl flows into the mold 11 without coming into contact with 02 in the outside air.

As shown in Fig. 6, the pouring start tube 2a is a short tube with a cylindrical shape, and prevents the molten metal (9) from solidifying and adhering to the nozzle at the start of pouring, and also secures the amount of molten metal at a predetermined height in the tundish. After that, in order to discharge the molten metal in a state close to a steady flow, it is fitted into the discharge port so as to protrude into the main body.

This casting start tube is generally made of steel or refractory material, and once the molten metal flows through its inner cavity, the former will melt and disappear, and the latter will be removed.

[Problems to be Solved by the Invention] In the continuous casting method, one of the problems when pouring molten metal from a ladle into a mold is oxidation of the molten metal due to the atmosphere.
This problem is particularly serious in molten steel containing metals that are easily oxidized, such as AR-killed steel. One of the places where oxidation occurs is in the tundish, which is located between the steel stock and the mold. In the tundish, the molten metal is spread once and distributed to each mold, so it has a large contact area with the atmosphere and is greatly affected by the atmosphere, which is especially a problem at the start of pouring. Therefore, various measures have been taken to prevent oxidation here. One of the countermeasures is to create a reducing atmosphere by blowing Ar gas into the tundish at the start of casting.This method lowers the 02 in the atmosphere at the start of casting, as shown in Figure 8. More than 10% of 02 still remains, and 213 acts as an antioxidant.
The results are insufficient. This is because the tanditshu has various holes necessary for work, such as a hole for inserting a gas burner to preheat the tanditshu, and even if the
This is because even if r gas is blown in, air from the outside enters and 02 in the atmosphere is not completely removed.

As a result, at the early stage of casting, as shown in Fig. 4 as a conventional method, the sol in the molten steel sampled from the mold directly below the casting nozzle.

The A I (soluble aluminum) value is the sol, A rl of the raw steel sample taken from below the cast steel.
Compared to the value, this depleted sol, A Q
becomes Al2O2 and remains as an inclusion in the slab, severely damaging the steel quality of the slab (description of drawings will be described later in Examples).

Therefore, another method is to start blowing Ar gas earlier, and to apply Ar gas to the tundish from the time when preheating is completed.
Attempts have been made to make the atmosphere inside the tundish reducible by blowing in r gas and closing all the holes in the ceiling of the tundish.

However, one such hole that is difficult to close is the discharge port. As shown in Fig. 5, the casting nozzle 7 connected to the discharge port 6 consists of a sliding nozzle 8 and an immersion nozzle 9, and is open at the start of casting, so it is not airtight and the casting starts. Until the molten metal completely blocks this area, outside air can enter through this area. However, this area must be kept open to prevent the initial molten metal from solidifying and adhering, and cannot be completely blocked.

The present invention includes a tundish main body into which molten metal is supplied and a molten metal discharge port formed at the bottom, a sliding nozzle installed under the discharge port to adjust the flow rate of the molten metal, and a tundish body that protrudes into the main body. and a casting start pipe fitted into the discharge hole, and when the amount of molten metal in the main body exceeds the protruding height of the casting start pipe, the molten metal is discharged from the discharge port. An object of the present invention is to provide a tundish for continuous casting that prevents outside air from entering from a casting start pipe in order to seal the inside of the tundish.

[Means for Solving the Problems] In the continuous casting tundish according to the present invention, the casting start pipe has an airtight lid that closes the inner cavity thereof, and prevents outside air from entering the main body. This is a tundish for continuous casting.

[Function] By closing the casting start pipe with the airtight lid as described above, the intrusion of outside air from the discharge port into the tundish at the time of starting casting is completely prevented, and the above-mentioned result is completely prevented. By using this method in combination, it is possible to create a reducing atmosphere in the tundish at the start of casting.

At the point when the molten metal flows down the discharge port, the casting start tube is melted or removed, so that it does not impede the molten metal flow. Note that from this point on, as described above, oxidation of the molten metal flow does not occur.

[Example] Fig. 1 shows a tundish 1 for continuous casting according to the present invention. The tundish 1 includes a refractory wall 14, a discharge port 6 that passes through the bottom of the wall 14, and a sliding nozzle 8 that is installed below the refractory wall 14. and a casting nozzle 7 consisting of an immersion nozzle 9, a casting start pipe 3 fitted into the discharge port 6, and a ceiling 15.
A hole 17 for inserting a gas burner for preheating the gas, an insertion port 16 for an Ar gas blowing pipe, and a few holes (other holes are not shown) are open.

The pouring start pipe 3 prevents a trickle of relatively low-temperature molten metal from flowing into the pouring nozzle 7 and solidifying on the sliding nozzle 8 at the start of pouring, and secures a predetermined height of molten metal in the tundish 1. In order to discharge the molten metal 10 all at once for the first time after the casting process, the casting start pipe 2 of the present invention is fitted into the discharge port 6 so as to protrude from the bottom of the inner wall 14 by a predetermined height. 4 is closed with a lid body 5,
This prevents outside air from entering through this area.

The casting start tube 2 consists of a short cylindrical tube 3 in the same shape as the conventional casting start tube 3a (FIG. 6) and a lid body 5.
In this embodiment, steel is used as the material. The lid body 5 is a flat disc, and its circumferential portion is attached to the inside of the tube 3 in the middle of the tube 3 to ensure airtightness by closely contacting the inner surface of the tube 3, as shown in FIG. In addition to being shielded from the outside air, the thickness of the plate is thin enough to dissolve and disappear when the molten metal passes over the upper end of the tube 3 and flows into the inner cavity 4. Therefore, this lid body 5 does not obstruct the subsequent flow of the molten metal.

FIG. 3 shows the results of one example in which casting was carried out using the tundish 1 equipped with the casting start tube 2 according to the present invention, together with the other sealing methods described above, and the procedure was as follows: - After installing the casting start tube 2, the tundish 1 is preheated and dried with a gas burner. - Once the preheating is completed, the gas burner is handled, the hole 17 is sealed with the lid 18, and the other holes are sealed in the same manner. - Immediately insert the Ar gas pipe into the insertion port 16 and start blowing Ar gas. - After about 6 minutes, move the tundish 1 onto the mold 11, start casting, and start blowing Ar gas. Stop.

According to the above procedure, 021! As shown in the figure, the percentage is 0 to 2% throughout the period, and the difference is clear when compared with FIG. As a result, the oxidation of the molten metal 10 by the atmosphere 13 was significantly reduced, and in several repeated examples, as shown by 10- in FIG. The amount of decrease is stably 5 or less, and the sol when casting is performed by the above-mentioned conventional method.

Compared to the decrease in A°C (the rectangular range surrounded by solid lines in the figure), inclusions in the slab were clearly reduced. still,
Figure 6 is a diagram showing how sol and Aβ in molten steel sampled from the mold 11 directly below the pouring nozzle change depending on the casting time. (refers to the length of the slab from the surface of the molten steel in the mold 11 to the dummy bar head from which the slab is pulled out), and the oxidation degree of the molten steel is expressed by the difference in Sol and A fi between the raw steel and the above-mentioned sample on the vertical axis. It shows.

[Effects of the Invention] As described above, the tundish of the present invention protects the sliding nozzle attached to the bottom of the tundish and enables smooth casting, and when used together with other sealing methods, the tundish can be completely sealed. The atmosphere is reduced, making it possible to produce slabs with fewer inclusions such as Affi20a.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of the tundish according to the present invention, FIG. 2 is a perspective view of a casting start pipe attached to the tundish, and FIG. 3 is an embodiment of the tundish according to the present invention. , a progress chart showing the change of 021 degrees in the atmosphere in the tundish, and Fig. 4 shows the sol, A, Q, and Figure 5 is a conceptual diagram showing a cross section of a tundish with a conventional casting start pipe attached, Figure 6 is a perspective view of a conventional casting start pipe without a lid, and Figure 7 is a diagram showing changes depending on the casting period. Fig. 8 is a conceptual diagram showing the situation in which molten metal flows into the mold while being blocked from the surrounding air.
It is a progress chart showing the change of i1 degree. 1... Tanditshu, 2... Casting start pipe, 5.
... Lid body, 6... Discharge port, 7... Casting nozzle, 8
...Sliding nozzle, 9...Immersion nozzle, 1
1... Mold, 15... Ceiling.

Claims (1)

[Claims] a tundish main body into which molten metal is supplied and a molten metal discharge port formed at the bottom; a sliding nozzle installed below the discharge port to adjust the flow rate of the molten metal; In the continuous casting tundish, the continuous casting tundish has a casting start pipe fitted into the continuous casting tundish and discharges the molten metal from the discharge port when the amount of molten metal in the main body exceeds the protruding height of the casting start pipe. A tundish for continuous casting, characterized in that the starting tube has an airtight lid that closes the inner cavity of the starting tube, and blocks outside air from entering the main body.