JPH0760419A - Method for preparation of casting - Google Patents

Abstract

PURPOSE:To stably open the hole in a nozzle by closing a sliding nozzle after flowing out a plugged material in an upper nozzle together with molten steel and blowing gas into the molten steel in the upper nozzle. CONSTITUTION:The sliding nozzle composed of the upper nozzle 1 and upper and a lower plates 3, 4 for the sliding nozzle is arranged at the bottom part of a molten steel ladle laid on a supporting device for molten steel ladle. This sliding nozzle is opened and the material beforehand packed in the upper nozzle 1 is allowed to flow out together with the molten steel from the molten steel ladle. Thereafter, the sliding nozzle is closed and successively, gas is blown into the molten steel in the upper nozzle 1 from the lower plate 4 for the sliding nozzle through a gas blowing pipe 5. By this method, the solidification of molten steel in the nozzle can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting preparation method for continuous casting equipment.

[0002]

2. Description of the Related Art To improve productivity in continuous casting,
It is an effective means to carry out so-called continuous casting operation in which continuous casting is connected by exchanging molten steel ladle.

Looking at the quality of the slabs produced by ladle-exchange continuous casting, as compared with the quality of the slabs of the stationary part, the top slab, the bottom slab and the seam of the continuous slab, which are the slabs of the unsteady part, The quality level is low (Fig. 1).

The deterioration of the quality of the unsteady cast slabs is caused by the slag that the nozzle filling drops into the tundish from the molten steel ladle and mixes in the molten steel when the molten steel ladle is opened, or floats on the molten steel surface in the ladle or tundish. It is considered that the reason is that the inclusions are involved, or inclusions that are floating in the molten steel are cast.

As described in JP-A-4-228247, the quality of the bottom part or the seam part of the unsteady cast piece deteriorates, as described in JP-A-4-228247. The filler (stuffing sand, etc.) filled in the (steel tap) drops into the tundish and is suspended in the molten steel, or SiO ₂ which is a constituent of the filling sand causes oxides such as Al in the molten steel to be removed. It is also caused by being injected into the mold from the tundish through the immersion nozzle, cast, and collected as inclusions in the slab.

Further, when performing the injection without using the injection flow sealing device between the molten steel ladle and the tundish, if the molten steel solidifies in the injection nozzle and the molten steel passage in the flow rate control device, it causes it. Turbulence occurs in the injection flow, causing oxidation of molten steel by the atmosphere and increasing oxides in the molten steel.

As a method for preventing the filling sand of the nozzle from deteriorating the quality of the slab, in Japanese Patent Laid-Open No. 4-228247, the filling sand filled in the injection hole (steel tap) of the molten steel pot before casting is used. A method of discharging is described (Fig. 2
4).

The work shown in FIGS. 2 to 4 is referred to as an initial opening work, and is performed as a pre-work for the molten steel injection work into the tundish.

The molten steel pouring work into the tundish is shown in FIG.
After the initial drilling work based on No. 4, the molten steel ladle is transferred to the tundish and carried out.

It is important to prevent mixing of the nozzle filling into the molten steel casting from the viewpoint of slab quality, but the nozzle filling is originally an injection work when a sliding nozzle is used as a device for controlling the injection flow rate of the molten steel ladle. In order to prevent molten steel from flowing out of the pan when the nozzle is opened, or to prevent solidification of molten steel in the nozzle.

Therefore, after discharging the nozzle filling,
When the nozzle opening cannot be performed normally by the opening operation of the sliding nozzle at the casting position, that is, when molten steel solidification occurs in the nozzle and nozzle clogging occurs, the molten steel in the nozzle is melted by oxygen. Since it is necessary to take measures such as opening holes, the operation is impeded, and at the same time, the molten steel is oxidized, which causes a problem in terms of quality of the slab.

In Japanese Patent Laid-Open No. 4-228247, as a countermeasure against nozzle clogging after the initial opening (filling is discharged from the nozzle portion), the filling (filling sand) is discharged, and then a gas is blown from the sliding nozzle plate. However, a method for preventing molten steel solidification at the nozzle portion is described.

However, according to the experience of the present inventor, even if the method described in the publication is carried out, it is not sufficient to stably prevent the solidification.

That is, before discharging the filler, a part of the molten steel in contact with the refractory material in the nozzle portion is solidified. Moreover, the molten steel near the nozzle is low-temperature molten steel whose temperature has been deprived by the surrounding refractory material.

Immediately after discharging the filler, the molten steel that has entered the upper nozzle has a low temperature and contacts the refractories of the upper nozzle and the sliding nozzle, which have a lower temperature than the molten steel,
The molten steel that has absorbed heat or the like and has entered the nozzle subsequent to the discharge of the filling material is in a state of being easily solidified.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 4-228247, only the filling material is discharged, the nozzle is immediately closed, and the gas is blown from the closing plate. The phenomenon in which the molten steel solidifies on the plate surface of the sliding nozzle cannot be completely prevented, and the nozzle is highly likely to be blocked.

[0017]

DISCLOSURE OF THE INVENTION The present invention provides a method for facilitating the opening of the injection hole in the upper nozzle at the casting position after discharging the filling material in the upper nozzle, and in the continuous casting operation. (EN) A method capable of preventing molten steel from solidifying in a nozzle even after discharging a nozzle filling and stably opening a nozzle during casting.

[0018]

According to the present invention, in continuous continuous casting operation, when the molten metal ladle nozzle is discharged before casting, the ladle is moved to the casting position on the tundish to perform the pouring operation. Moreover, the molten steel is prevented from solidifying in the nozzle, and the nozzle can be stably opened.

That is, according to the present invention, the sliding nozzle is placed at the molten steel ladle supporting device and has the upper nozzle and the sliding nozzle at the bottom, the sliding nozzle is opened at the initial opening position of the molten steel ladle, and the upper nozzle is injected into the injection hole. The filling material (stuffing sand etc.) filled in advance is discharged and molten steel is caused to flow out, and the temperature of the upper nozzle and the sliding nozzle plate is raised.

After flowing out the molten steel in an amount capable of heating the upper nozzle or the sliding nozzle plate above a preset temperature, the sliding nozzle is closed to interrupt the injection flow, and then gas is blown from the sliding nozzle plate. A casting preparation method for preventing molten steel from solidifying in a nozzle.

In particular, as a method for detecting the temperature rise of the refractory material of the upper nozzle or the sliding nozzle plate, a detecting end for measuring the temperature is embedded in the sliding nozzle plate or the refractory material of the upper nozzle to form a molten steel ladle. It is advisable to continuously measure the refractory temperature from the start of opening. Then, the injection flow is interrupted when the refractory temperature reaches a preset temperature.

In this case, the temperature measured at the detecting end depends on the sliding position of the detecting end in the sliding nozzle plate or the refractory of the upper nozzle, or the operating condition of the pan or sliding nozzle (continuous use, intermittent use). Etc.).

The measured temperature is heated by the molten steel and tends to rise with the amount of molten steel passing through the nozzle portion.

When the temperature at a specific measuring position exceeds a certain temperature, the refractory in the portion in contact with the molten steel is sufficiently heated by the molten steel, the sliding nozzle is closed, and gas is blown from the sliding nozzle plate. However, it is possible to prevent the molten steel from solidifying in the nozzle even while waiting.

If the temperature for judging the closing of the sliding nozzle becomes higher, the nozzle opening rate at the casting position increases.

However, since the amount of discharged molten steel at the time of initial opening is large, the casting yield is reduced.

Therefore, in the operation standard, the detection end embedding position is specified, and the closing temperature of the sliding nozzle is determined as a temperature at which the temperature measured at that position can compensate for the nozzle opening ratio of 95% or more at the tundish injection position. Set as temperature.

The above-mentioned preset temperature refers to a temperature set based on such a concept.

[0029]

Embodiment 1 FIGS. 5 to 7 show an embodiment in which a temperature detecting end is provided on a sliding nozzle upper plate.

An R thermocouple was used as the temperature detecting end.

The sliding nozzle has a diameter of 90 mm (L
The 2 plate type of 1) is used and the embedded position of the temperature detection end is 15 mm from the outer edge of the nozzle opening of the upper plate.
The position is separated by (L2).

FIG. 8 shows the temperature side determination result at the above position.

Arrows indicate variations in measured temperature, and circles indicate average temperature.

The molten steel injection amount indicates the amount of molten steel that has been continuously discharged after discharging the filling material in the nozzle.

As shown in FIG. 8, in the molten steel injection amount range of this time, the refractory temperature at the temperature measuring position tends to increase as the molten steel injection amount increases.

Further, when the molten steel injection amount is within 0.5 ton, the refractory temperature has a large variation, and when the molten steel is injected more than that, the temperature variation is small and stable.

The solidification state of the molten steel at the nozzle portion is affected by the conditions under which the pot is used. When the molten steel solidifies at the nozzle portion, after the filler is discharged, the molten steel outflow from the nozzle is obstructed and the injection flow is narrowed.

As a result, the molten steel is discharged from the nozzle without raising the temperature of the upper nozzle and the sliding nozzle plate.

Since the temperature of the upper nozzle and the sliding nozzle plate is low at the initial stage of the nozzle opening, the molten steel outflow amount is not stable and the temperature tends to vary widely.

However, when the molten steel is continuously discharged, the temperature of the upper nozzle and the sliding nozzle plate rises, the injected flow is rectified, and the temperature variation is stably reduced.

FIG. 9 shows the relationship between the amount of molten steel injected after discharging the filling sand and the nozzle opening ratio at the casting position.

When the molten steel injection amount is increased from FIG. 9,
It can be seen that the porosity is improved, and stable porosity can be achieved even at the casting position by allowing 0.5 ton or more of molten steel to flow out at the initial opening position.

The hole opening work at the casting position was performed after 6 to 25 minutes had passed from the initial hole forming work.

From FIGS. 8 and 9, if the refractory temperature at the measuring position is 700 ° C. or higher, or the molten steel injection amount is 0.5 ton or higher, the nozzle porosity at the casting position is 95%.
A stable opening capable of compensating for more than 100% is possible.

[0045]

Embodiment 2 FIGS. 10 to 11 show an embodiment in which a temperature detecting end is provided on the upper nozzle.

Also in this case, the nozzle filling is discharged together with the molten steel at the time of the initial opening, and the temperature of the refractory at the temperature measurement point reaches a preset temperature by increasing the temperature of the refractory by the molten steel flowing out. Close the sliding nozzle,
Gas is blown into the nozzle from the sliding nozzle plate to prevent the molten steel in the nozzle from solidifying, so that stable holes can be formed during casting.

[0047]

As described above, according to the present invention, it is possible to prevent the molten steel from solidifying in the nozzle and stably open the nozzle during the casting performed after discharging the nozzle filling in the continuous casting operation.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the quality of each part of a slab produced by continuous casting.

FIG. 2 is an explanatory view showing an initial opening work state of a molten steel ladle (before initial opening).

FIG. 3 is an explanatory view showing an initial opening work state of the molten steel ladle (during initial opening).

FIG. 4 is an explanatory view showing an initial opening work state of a molten steel ladle (standby (during gas blowing)).

FIG. 5 is an explanatory view showing an initial opening work situation (at the time of initial opening) in the case of the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an initial opening work state (at the time of standby) in the case of the first embodiment of the present invention.

FIG. 7 is an explanatory view showing an initial opening work situation (temperature detection end mounting position) in the case of the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the relationship between the molten steel injection amount and the refractory measurement temperature at the detection end setting position during the initial opening work.

FIG. 9 is an explanatory diagram showing a ladle nozzle opening rate at a casting position after performing an initial opening operation.

FIG. 10 is an explanatory view showing an initial opening work situation (at the time of initial opening) in the case of Embodiment 2 of the present invention.

FIG. 11 is an explanatory diagram showing an initial opening work situation (at the time of standby) in the case of the second embodiment of the present invention.

[Explanation of symbols]

 1 Upper Nozzle 2 Tuyere Brick 3 Sliding Nozzle Upper Plate 4 Sliding Nozzle Lower Plate 5 Gas Injection Pipe 6 Temperature Detection End (Thermocouple) 7 Nozzle Filler 8 Molten Steel 9 Gas Bubble L1 Nozzle Diameter L2 Distance to Embedding Position

Claims (3)

[Claims] 1. An upper nozzle mounted on a molten steel ladle supporting device,
From the molten steel ladle having a sliding nozzle at the bottom, open the sliding nozzle, and let the filler pre-filled in the upper nozzle flow out together with the molten steel, then close the sliding nozzle, and then continue from the sliding nozzle plate to the upper nozzle. A method for preparing for casting, which comprises blowing gas into molten steel. 2. The sliding nozzle plate is embedded with a detection end for measuring the refractory temperature, the sliding nozzle is opened, and the prefilled material in the upper nozzle is allowed to flow out together with the molten steel so as to adjust the refractory temperature. The continuous measurement, when the refractory temperature reaches a preset temperature, the sliding nozzle is closed to interrupt the injection flow, and then the gas is blown from the sliding nozzle plate. Casting preparation method. 3. The refractory is embedded in a molten steel ladle upper nozzle portion with a detection end for measuring the temperature of the refractory material, the sliding nozzle is opened, and the filling material pre-filled in the upper nozzle is discharged together with the molten steel. Continuously measuring temperature,
The casting preparation method according to claim 1, wherein when the refractory temperature reaches a preset temperature, the sliding nozzle is closed to interrupt the injection flow, and then the gas is blown from the sliding nozzle plate.