JPH03243256A - Sequentially continuous casting method using long nozzle - Google Patents

Abstract

PURPOSE:To prevent contamination of molten metal in a tundish by supplying non-oxidizing gas from a vent hole before pouring the molten metal from a ladle, making the excessive pushing-out pressure with the equation the specific value or higher and discharging remaining slag in a long nozzle. CONSTITUTION:The non-oxidizing gas of N2, Ar gas, etc., is blown from the vent hole 6 of the long nozzle 3, and the remaining slag in the long nozzle 3 is pushed to outside. Then, gas blowing pressure P is selected so that the excessive pushing-out pressure shown with the equation P=PG-rhoh comes to >=1.5kg/cm<2>. In the equation, PG: gas blowing pressure (kg/cm<2>), rho: sp. gr. of molten metal (kg/cm<3>), h: submerged depth of the long nozzle (cm). By this method, the contamination of molten metal in the tundish with the remaining slag in the long nozzle and the slag in the preceding ladle can be prevented.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a continuous casting method using a long nozzle, and particularly to a continuous casting method that can discharge slag from a preceding ladle remaining in the long nozzle to the outside of the molten metal. This invention relates to a continuous casting method.

<Prior art> In the continuous casting method, as shown in FIG. 7, a long nozzle 3 is generally used for the purpose of preventing atmospheric oxidation of the molten metal when pouring the molten metal 4 from the ladle 1 to the kundishu 2. It is used in

At this time, as shown in Fig. 7, there is residual slag 5 in the long nozzle that has flowed out from the preceding ladle 1a where the injection was completed earlier.
is accumulating. When the molten metal 4b is injected from the subsequent ladle 1b while this residual slag 5 remains, the residual slag 5 in the long nozzle 3 is pushed out of the long helix by the injection flow of the 1-volume molten metal 4b into the tundish. However, there was a problem in that the molten metal 4a of the tundish was diffused over the width of the molten metal 4a, contaminating the molten metal 4a.

<Problems to be Solved by the Invention> The present invention solves the above-mentioned problems of the prior art, and provides a continuous continuous method using a long nozzle that can suppress the turbidity of molten metal in the kundish due to slag in the ladle and residual slag. This was done to provide a casting method.

<Means for Solving the Problems> The present invention uses a long nozzle between a ladle and a kundishu, and when injecting molten metal from the ladle into the kundishu, the inside of the long nozzle immersed in the molten metal in the tundish. In order to discharge the residual slag from the preceding ladle that remains in the ladle, a vent hole that can supply gas is provided inside the long nozzle, and the upper end surface of the long nozzle is placed between the lower end surface of the lower nozzle and the slide nozzle of the succeeding ladle. - After making a close contact via a plastic heat-resistant sealing material and before injecting molten metal from the subsequent ladle, non-oxidizing gas is supplied from the vent hole to increase the pressure inside the long nozzle and reduce the excessive extrusion pressure P. 1.5kg/c+f1
This is a continuous continuous casting method using a long nozzle characterized in that after the residual slag is discharged as described above, injection from a subsequent ladle is started.

Here, P=P, -ρ・h ------11) P
G: Gas blowing pressure (kg/cJ), ρ: Specific gravity of molten steel (kg/cnl), h: Long nozzle immersion depth (cm).

<Function> FIG. 1 shows a cross-sectional view of the long nozzle used in the present invention connected to the lower end surface of the lower nozzle of the subsequent ladle, and FIG. 2 shows a conceptual cross-sectional view showing the residual slag discharge arm.

As shown in FIG. 1, a long nozzle 3 is used which is equipped with a vent hole 6 that can supply gas inside the long nozzle. In order to prevent the blown gas from leaking above the long nozzle, the ladle slide nozzle is closed, that is, the holes in the fixed plate 7a and the sliding plate 7b are shifted, and the upper end surface of the long nozzle and the bottom of the ladle slide nozzle are closed. A vertical plastic heat-resistant sealing material 8 is sandwiched between the nozzle 7c and the lower end surface.

A non-oxidizing gas such as N2 or Ar gas is blown through the ventilation hole 6 with the lower end surface of the lower nozzle 7 (and the upper end surface of the long nozzle 3 in close contact with each other).

At this time, in order to push out the residual slag 5 and molten metal inside the long nozzle 3 whose lower part is immersed in the molten metal 4a inside the long nozzle 3, the inside of the long nozzle is made to have a sufficiently high non-oxidizing gas pressure. By,
The residual slag in the long nozzle is pushed out and quickly floats above the molten metal 4a in the kundish due to the difference in specific gravity with the molten metal and together with the bubbles of the top-blown gas. Therefore, it is possible to prevent residual slag from diffusing into the molten metal and contaminating the molten metal, as in the prior art.

Here, if the gas injection pressure P is selected so that the excess extrusion pressure P shown in equation (1) above is 1.5 kg/cJ or more, the residual slag will completely float above the molten metal and be removed from the molten metal. is discharged.

<Example> The present invention was carried out in a continuous casting facility with a ladle capacity of 1230 tons and a tanday 7-shu capacity of 1170 tons. Table 1 shows the specifications of the long nozzle used.

FIG. 3 shows the thickness distribution of the slag remaining in the long nozzle at the time when the injection of the preceding ladle was completed. According to this measurement result, about 2 to 3 kg of slag remains in the nozzle. Note that the amount of residual slag increases or decreases depending on the timing of the slide nozzle closing operation at the end of pouring into the preceding ladle.

FIG. 4 shows the relationship between the blowing gas pressure, the gas blowing time, and the slag discharge rate. Here, the slag discharge rate is a value calculated using the following formula.

A: Residual slag thickness at the end of injection (M), B: Residual slag thickness after adoption of the method of the present invention (mm).

From FIG. 4, in order to discharge the residual slag, it is necessary to carry out the blowing gas pressure at 2 kg/c- or more and the blowing time at 10 seconds or more.

FIG. 5 shows the relationship between extrusion overpressure and slag discharge rate so that the above results can be applied to other equipment.

Here, the extrusion excess pressure P (kg/cIll) is determined by the following formula.

P=PG~ρ・h −11−−−−(
]) PG: Gas blowing pressure (kg/c++1), ρ
: Melt specific gravity (kg/c!), h : Long nozzle immersion method height (cm), (see Figure 1).

It can be seen from FIG. 5 that the effect is significant when the extrusion overpressure is 1.5 kg/cj or more.

Figure 6 shows the method of the present invention (P: 2-2.5 kg/c
The ratio of the total oxygen concentration in the inner steel of the tundish in the low-aluminum killed steel with and without the conventional method is shown. As is clear from the figure, it can be seen that the method of the present invention improves the total oxygen concentration in the steel.

Here, the total oxygen concentration index in the inner steel of the tanditshu is a value calculated by the following formula.

Table 1 Total Oxygen Concentration Index in the Steel Inside the Kunditsu <Effects of the Invention> According to the method of the present invention, as mentioned above, it is possible to completely prevent the contamination of the molten metal in the Kunditsu due to the residual slag in the long nozzle and the slag in the preceding ladle. can.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the long nozzle used in the present invention connected to the lower end surface of the lower nozzle of the succeeding ladle, and Fig. 2 shows the state of discharge of residual slag in the long nozzle before pouring into the succeeding ladle by the method of the present invention. Fig. 3 is a histogram showing the thickness distribution of the residual slag in the long nozzle at the end of the preceding ladle injection in the example, and Fig. 4 shows the blowing gas pressure and gas blowing time in the example. Figure 5 is a characteristic diagram showing the relationship between the slag discharge rate and Fig. 6.
The figure is a histogram showing the total oxygen concentration index in the steel inside the tundish. Figure 7 is a conceptual cross-section when a long nozzle for oxidation prevention of molten metal injection flow is used between the ladle and the tundish in a continuous continuous casting method of molten metal. In the figure, (a)
(b) shows after the preceding ladle has finished casting, and (b) shows before the succeeding ladle starts casting. 4a... Molten metal in the kundishu, 4b... Molten metal in the ladle, 5... Residual slag, 6... Ventilation hole, 7a... Slide nozzle fixing plate, 7b... Slide nozzle sliding Plate, 7c...Slide nozzle lower nozzle, 8...Elastic/plastic heat-resistant sealing material, 9...Slag in ladle. 1a...Advanced ladle, Ib...Following ladle, 2...Tandish, 3...Long nozzle,

Claims (1)

[Claims] A long nozzle is used between the ladle and the tundish,
When pouring molten metal from the ladle into the tundish, gas is supplied to the inside of the long nozzle to discharge residual slag from the preceding ladle that remains in the long nozzle immersed in the molten metal in the tundish. Provide ventilation holes that allow
After the upper end surface of the long nozzle is brought into close contact with the lower end surface of the lower nozzle of the slide nozzle of the succeeding ladle via an elastic/plastic heat-resistant sealing material, before injecting molten metal from the succeeding ladle, a non-oxidizing A long nozzle characterized by supplying gas to increase the pressure inside the long nozzle, increasing the excess extrusion pressure P to 1.5 kg/cm^2 or more, discharging the residual slag, and then starting injection from the subsequent ladle. Continuous continuous casting method using a nozzle. Here, P=P_G−ρ・h……(1) P_G: Gas blowing pressure (kg/cm^2), ρ: Molten steel specific gravity (kg/cm^2), h: Long nozzle immersion depth ( cm).