JPS61119358A - Continuous casting method - Google Patents

Abstract

PURPOSE:To improve product quality by segmenting a tundish to a receiving chamber and tapping chamber by a longitudinal gate and supplying a molten steel to the receiving chamber while maintaining approximately the specified molten metal level in said chamber. CONSTITUTION:The gate 7 extending longitudinally is provided to the tundish 3 to form the receiving chamber 4 and the tapping chamber 5. A communicating hole 10 is disposed in the lower part of the gate 7. The molten metal in the previous ladle 1 is poured into the tundish 3, then the molten metal enters first the chamber 4 and is conducted through the communicating hole 10 of the gate 7, then through the chamber 5 to a mold 8. the pouring to the chamber 4- of the succeeding ladles 2 is started before the pouring of the previous ladle 1 is finished. The pouring to the mold 8 is thus executed while the approximately the specified molten metal level is maintained. since the inclusion in an ingot is considerably decreased by the above-mentioned method, the product quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a continuous casting method for efficiently producing continuously cast slabs with high cleanliness.

Conventional technology In continuous casting of steel, in order to increase productivity and improve yield, it is necessary to continuously cast, that is, to continuously produce slabs without interruption by sequentially bringing pots filled with molten steel onto the continuous casting machine mold. It is necessary to.

In operations where molten steel is conveyed in a ladle from a melting furnace to a continuous casting machine and continuously cast, a buffer container called a tundish is used to connect the molten steel supplied in batches to continuous slabs.

In the conventional method, the supply of molten steel was interrupted when the ladle was replaced, which caused operational and quality problems.

Regarding this matter, there are many known examples (for example, Utility Model Act 413
-42846), but when molten steel is poured into the receiving part of a tundish from one ladle and casting is continued after the pouring of this ladle is finished, the pouring is interrupted until the next ladle arrives.

(For example, it usually takes 2 to 3 minutes to change the ladle using the one-dollar turret method, and 3 to 5 minutes when changing the ladle using the one-dollar turret method.) This interruption in the supply of molten steel causes a drop in the molten steel level in the tundish, causing a When pouring into the ladle starts, slag, deoxidation products, etc. existing on the free surface of the molten steel in the tundish are violently thrown into the molten steel flow and mixed into the molten steel, resulting in a decrease in the cleanliness of the slab. vinegar.

In order to prevent this, a method was devised in which while pouring from one ladle of the tundish, the molten steel could be poured from the next ladle while maintaining the molten steel level at a constant level (Japanese Patent Laid-Open No. 57-1
24558).

However, if the injection point from the ladle and the outflow point to the mold are located close to each other in a single-chamber container, there is a risk that molten steel from the ladle may flow into the mold in a short-circuit manner, and non-metallic inclusions may occur in the tundish. Separation by flotation cannot be expected, so the level of inclusions in the steel is high and the cleanliness is poor.

Problems to be Solved by the Invention The present invention eliminates the quality defects of conventional full-type tundishes and efficiently produces continuously cast slabs with high cleanliness. The present invention provides an i-continuous casting method.

Means for Solving the Problems In order to eliminate the above-mentioned inconveniences, the present invention provides a weir running vertically in the longitudinal direction of the tundish, as shown in FIG. The molten steel in the tundish was divided into two chambers, and the molten steel in the tundish was designed to be able to receive molten steel from two pots at the same time so that the level of hot water in the tundish remained constant even when changing pots, and the molten steel in the tundish was installed at a weir. Make sure it comes out through the communication hole.

There is no particular restriction on the location of the communication hole, but since two pots are brought in at the same time, it is preferable to place it near the center in the longitudinal direction for quality stability, and providing it at the bottom will prevent inclusions from floating in the tapping chamber. The effect is large and appropriate.

That is, if it is provided at the bottom, it is possible to prevent the slag on the upper surface of the hot water receiving chamber from flowing into the hot water tapping chamber. Regarding the size of the hole, it is necessary to ensure a cross-sectional area necessary for the passage of molten copper.

In addition, in order to further promote the inclusion removal effect in the tapping chamber, there are various methods for removing inclusions, such as blowing in a small amount of inert gas from the bottom, installing new inclusion adsorption groups, and removing inclusion powder. It is also useful to apply appropriate combinations of body inputs, etc.

action FIG. 1 shows a schematic diagram of the present invention.

1.2 is a pot for transporting molten steel tapped from the melting furnace, 3
is tandish. First, when the molten steel in the front ladle 1 is poured into the tundish, it enters the molten metal receiving chamber 4, and is led to the mold 8 through the central lower communication hole 10 of the weir 7, through the tapping chamber 5.

Before the end of pouring into the front pot 1, the next ja2 is transported from the melting furnace and pouring into the receiving chamber 4 is started. Thereafter, as the amount of hot water remaining in the front pot 1 decreases, pouring into the front pot is finished while reducing the amount of hot water poured in order to prevent slag from being mixed into the front pot due to the vortex phenomenon.

Casting is continued by repeating such pot replacement work, but since the supply of molten steel from the pots is not interrupted, the amount of pouring from both pots is appropriately controlled. It is possible to keep the surface constant.

In the present invention, in order to improve quality, the amount of slag flowing into the tundish can be minimized by inserting a slag stopper/par 9 before the amount of hot water remaining in the front pan decreases and slag is mixed in. It is possible.

In addition, when pouring molten steel from the ladle into the tundish, a refractory seal 6 is applied to prevent air oxidation, At is blown from a part of the refractory seal, and a filter is installed in the communication hole of the weir 7 that separates the hot water receiving chamber 4 and the hot water tapping chamber 5. (not shown) to clean the steel.

Since the flow of molten steel in the tapping chamber 5 is quiet, the free surface can be covered with a powdered steel refining agent (not shown) for further cleaning.

In addition, in FIG. 1, a part of the weir is cut away to show the state of injection from the nozzle.

EXAMPLE Low carbon aluminum guild steel having the composition shown in Table 1, tapped from a converter, was cast through a two-tank tundish of the present invention.

Table 1: Composition of low carbon aluminum killed steel The amount of molten steel per heat is 300 tons, and the total capacity of the two-tank tundish is 45 tons (first tank 22E, second tank 23L).

A refractory nozzle was used between the pot and the tundish to prevent air oxidation of the injected flow, and a weir was provided between the first and second tanks of the tundish to perform continuous five-pot casting.

When replacing the pot, we started pouring the next batch when the amount of hot water remaining in the front pot was 50 tons, and took care to keep the hot water level in the tundish constant.

The space between the tundish and molding 1 was degassed using an immersion nozzle, and normal powder casting was performed.

The casting size of the mold is 250 ma thick and 150 ha wide.
The casting speed was 1 m/min. From the immersion nozzle,
Ar was blown at a rate of 5 per minute to help float up inclusions within the mold.

On the other hand, for comparison, casting was carried out using a boat-shaped tundish (Fig. 2) under the same conditions as described above except for the tundish.

In the case of a full-type tundish, a pot 1, a tundish 3, and a mold 8 are arranged as shown in FIG. 2, and the space between the pot and the tundish is sealed with a long nozzle 2, and a weir 17 is provided inside the tundish.

In the case of all types of tundishes, it is not possible to pour into two pots at the same time, so when replacing the pots, the pouring will be interrupted for about 2 minutes. During this period, the amount of molten steel poured into the mold is approximately 10.5 tons, and the amount of molten steel in the tundish at the start of the first injection is 49.5 tons.

FIG. 3 compares the inclusion levels of slabs cast using the two different types of tundishes.

Effects of the Invention From FIG. 3, the two-tank type tundish has the following two superior points compared to the full-type tundish.

(1) Inclusions in the joint slabs when replacing the pot are greatly reduced.

(2) As the number of pans in continuous casting increases, inclusions increase in the upper right corner in all types of tundishes, but there is almost no such tendency in two-tank type tundishes.

As mentioned earlier, the improvement in quality when replacing the pot is due to a reduction in the amount of slag mixed in from the previous pot when replacing the pot, and a reduction in the amount of slag mixed in when starting the next batch of injection. Seem.

Next, regarding the fact that there is little quality deterioration even if the number of pots is repeated, there is a phenomenon in which pot slag generally flows into the tundish due to the vortex phenomenon at the end of pouring, and the slag oxidizes the molten steel in the tundish, causing quality deterioration. In the case of a two-tank tundish, there is almost no inflow of slag in the pot into the tapping chamber, so it is thought that there will be no quality deterioration even if the trivets are piled up.

As described above, the present invention is an extremely excellent continuous casting method that eliminates the quality defects of conventional full-type tundishes.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the present invention. FIG. 2 is a perspective view showing an embodiment of a single-tank type without a separation weir running vertically through the center as one of the conventional examples. FIG. 3 is an example showing the effect of removing inclusions in a comparison between the present invention and a conventional example. l, 211... Pot, 3-... Tundish, 4-... Hot water receiving room, 5... Hot water tap room, 6... Refractory seal, 7...
・Weir, 8・l111 mold, 9・Reference Φ stopper, 1
0... communication hole, 11... stopper, 12 @- long nozzle, 17 fight φ weir.

Claims (1)

[Claims] A weir is provided running vertically in the longitudinal direction of the continuous casting tundish to divide it into a receiving chamber and a tapping chamber, and the receiving chamber is supplied with molten steel from a molten steel ladle so that the molten metal level is approximately constant.
A continuous casting method characterized in that the hot water then enters a tapping chamber through a weir with a communicating hole and pours into the mold from the lower part of the tapping chamber.