JPH02220748A - Continuous casting method - Google Patents

Abstract

PURPOSE:To stably execute a casting without nozzle clogging and occurring the breakage of the nozzle by casting molten metal while heating the molten metal between the submerged nozzle and the inner wall of a mold. CONSTITUTION:On the position between the nozzle submerged part and the mold inner wall in the molten steel 3 poured in the water cooled copper mold 2 for continuous casting from the submerged nozzle 1, the casting is executed while heating it by irradiating plasma arc 5 from a plasma torch 4 disposed above the molten steel surface. By this method, heat supplement into the position cooled with the submerged nozzle 1 and the water-cooled copper mold 2 for continuous casting is efficiently executed and a trouble damaging the submerged nozzle caused by developing solidified shell on outer surface of the submerged nozzle is prevented.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention uses an immersion nozzle that can stably cast even thin-walled metal slabs without causing nozzle clogging or nozzle damage. This relates to a continuous casting method.

<Conventional technology and its challenges> In recent years, against the backdrop of the remarkable development of metal refining technology and casting technology, as well as the rise in labor-saving and energy-saving ideas, it has become possible to directly and continuously manufacture thin sheets from molten metal without going through the hot rolling process. Attempts have been made to achieve this goal, and various studies have been carried out aimed at its realization.

By the way, continuous casting of thin-walled slabs naturally requires the use of a mold with both ends open, in which the distance between both long sides is much narrower than that of a normal mold. However, if we try to continuously cast thin-walled slabs of sound quality by pouring the molten metal using the immersion nozzle, which is now very commonly used from the viewpoint of preventing oxidation of the molten metal and stabilizing the scene, In single molds, the immersion nozzle and the inner wall of the mold (long side inner wall) are too close to each other, so the molten metal existing between the immersion nozzle and the inner wall of the mold is cooled by both, forming a solidified shell, and the nozzle There was a risk of damage.

In particular, at the start of pouring, the temperature of the nozzle is low and heat is easily absorbed from the molten steel, so the risk of the above-mentioned trouble occurring was considered to be extremely high.

On the other hand, in order to avoid the above problem, if the diameter of the immersion nozzle is made smaller to ensure a distance between the immersion nozzle and the inner wall of the mold, nozzle clogging is likely to occur due to non-metallic inclusions adhering to the inner wall of the nozzle. As a result, it was inevitable that this would hinder continuous casting operations.

Therefore, when trying to continuously cast thin slabs by a hot water supply method using a submerged nozzle, conventional methods have been developed that allow for a sufficient distance between the submerged nozzle and the mold wall and that do not cause the problem of nozzle clogging. Based on the idea that development is necessary, the following proposals were made.

(a) As shown in Fig. 4 (Fig. 4(a) is a plan view, Fig. 4(b) is its
Figure (C) shows the BB sectional view), mold long side 1
A method of pouring metal into a top-bottom open mold having a funnel-shaped pouring part 13 that expands in the center and narrows the long side of the mold as it goes down toward the exit side of the slab. Showa 6
0-158955).

(b) First, the above-mentioned disadvantages caused by using a submerged nozzle are avoided by casting to a thickness thicker than a predetermined thickness in a continuous casting mold consisting of an endless band whose mold wall moves in the same direction at the same speed, and then A method of compressing the inside of a piece with rolls to a predetermined thickness while it is still in an unsolidified state (Japanese Patent Application Laid-Open No. 61-1937
No. 44).

However, in both of these methods, the size of the mold in the hot water supply section is made larger than the thickness of the final slab, ensuring a sufficient distance between the immersed part of the nozzle and the inner wall of the mold, and there is less risk of nozzle clogging. Although this method made it possible to apply a submerged nozzle of the same size, the following problems were still pointed out when considering application to actual work.

That is, in the method shown in item 81 above, in order to obtain the final thickness of the slab, the mold is formed into a funnel shape that becomes narrower toward the bottom, and the slab is squeezed and deformed within the mold.
The means shown in the above-mentioned item (a) are based on the premise that deformation is applied to the unsolidified slab, such as by compressing it with rolls to make it to a predetermined thickness once the slab comes out of the mold.
The solidified shell of an unsolidified slab is brittle due to its high temperature, and if too much stress is applied, it easily cracks, resulting in quality defects such as "internal cracks." Moreover, since sizing is required to finally make the slab a predetermined thickness, there is a problem in that the number of steps increases accordingly.

Therefore, the purpose of the present invention is to solve the above-mentioned problems and to solve the problem of nozzle clogging and nozzle breakage by continuous casting using a pouring method using an immersion nozzle to produce thin slabs of good quality. The objective was to provide a means for stable production without requiring a sizing process for cast slabs.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have repeatedly conducted various experiments and conducted research. In addition to being easily heated by irradiation, by using this plasma arc to heat the molten metal between the immersion nozzle and the inner wall of the mold, the temperature drop in the molten metal due to the cooling effect of the immersion nozzle and mold is alleviated, and the temperature drop in this area is alleviated. "The formation of solidified shells is suppressed, and stable casting operations can be maintained even when the distance between the immersion nozzle and the inner wall of the mold is small."

The present invention has been made based on the above-mentioned findings, etc. ``When performing continuous casting using a submerged nozzle, by casting the molten metal between the submerged nozzle and the inner wall of the mold while heating it with a plasma arc, thin-walled casting can be performed. Even when casting pieces, stable casting can be performed without being limited by the dimensions of the immersion nozzle or adversely affecting workability or quality of the slab.

As described above, the present invention prevents cooling of the molten metal located between the immersion nozzle and the mold by plasma arc heating, and even when continuously casting thin slabs, thick slabs can be cast without using irregular molds. The present invention is designed to maintain stable casting work while compensating the heat so that the heat distribution state is the same as when hot water is supplied to the slab. explain.

Fig. 1 is a schematic diagram illustrating an example of the continuous casting method according to the present invention. It shows that casting is being performed while heating the area between the facing walls of the mold by irradiating plasma arc 5 from a plasma torch 4 disposed above the surface of the molten steel. Note that the plasma arc may be generated by using the plasma torch 4 as one pole and the dummy par 6 as the other pole.

In this way, if continuous slab casting is carried out while heating the molten steel in the area between the nozzle immersion part and the opposite wall of the mold with the plasma arc, the molten steel in the area cooled by the immersion nozzle 1 and the continuous casting river water-cooled open mold 2 will be heated. thermal compensation is carried out effectively,
This eliminates the problem of a solidified shell forming on the outer surface of the immersion nozzle and damaging the immersion nozzle.

According to this method, when continuously casting thin slabs, a large-diameter immersed nozzle with less concern about nozzle clogging is used, and the distance between the nozzle immersed part and the inner wall of the mold is reduced, so that Even if the degree of heat removal from the molten steel increases, sufficient thermal compensation is possible to prevent a solidified shell from forming on the outer surface of the immersion nozzle. Therefore, using irregularly shaped molds,
Thin slabs of target dimensions can be directly and stably cast without using a mold with an inner dimension thicker than the target dimensions and deforming the slab to a predetermined dimension in a subsequent process.

In addition, in the present invention, the heating means for the molten metal is limited to plasma arc because there are other methods other than plasma arc irradiation that are practical for arc irradiation that can easily and quickly locally heat the molten metal in the air or in an argon atmosphere. This is because it has not been done. However, "high-frequency heating" may be considered as a means of heating the molten metal, but it is extremely difficult to locally heat only the desired part to high temperatures using this method, and it is difficult to control). Placing the coil is physically difficult.

In other words, in addition to the fact that plasma arc heating can easily control the high-temperature heating region of the molten metal by adjusting the arc spot and irradiation distance, it is also fully applicable in the atmosphere or argon atmosphere where a submerged nozzle is used.
It has irreplaceable advantages.

The arc spot and irradiation distance of the plasma arc irradiated onto the molten metal surface may be adjusted as follows.

That is, FIG. 2 shows an example of the arc spot movement locus 8 during continuous casting of thin-walled slabs. (The size of the arc spot is approximately the same as the distance between the nozzle and the mold, and the size of the arc spot can be freely adjusted by adjusting the argon flow and voltage.) The arc spot is moved along the mold to uniformly heat the area near the nozzle. is good.

In this way, no solidified shell is formed between the mold and the nozzle, and it is possible to operate with a small heat load on the mold. On the other hand, if you try to make the arc spot wider in order to widen the arc irradiation area, the center of the arc will hit the mold surface, which could heat up the mold and cause melting damage, so avoid this. Should.

As a specific means for moving the arc irradiation surface, the plasma torch may be rotated around a fixed axis, and the gun tip may be moved toward the irradiation surface. Further, although the molten metal is particularly susceptible to cooling near the mold, cooling in the vicinity of the mold can be effectively prevented by making the end of the arc spot slightly touch the mold as shown in FIG. The moving distance of the arc spot in the longitudinal direction of the mold is most thermally effective when it is about 1.5 to 2 times the nozzle diameter.

The electric power transferred to the arc should be kept at a level that can thermally compensate for the formation of a solidified shell in the molten metal between the mold and the nozzle.
It is best to avoid making the diameter larger than this, as this will increase the heat load on the mold and lead to damage to the mold.

Here, an example of a suitable plasma arc heating means for carrying out the present invention is as follows.

i) Plasma torches (
For example, an argon arc plasma torch (as shown in FIG. 3) is provided.

ii) Using the plasma torch as one pole and the molten metal surface (dummy bar) as the other pole, a potential is applied between them and the molten metal is irradiated with plasma.

iii) By adjusting the angle of the plasma torch, the argon flow, etc., the size and position of the arc spot are determined so as to cover the nozzle immersion part and the mold wall part.

iv) The arc spot is made to move in an oscillating manner so that the irradiation surface is not fixed.

Next, the effects of the present invention will be explained in more detail with reference to Examples.

<Example> Using a continuous casting apparatus as shown in FIG. 1, a casting test of thin-walled steel slabs was carried out.

First, as an example of the present invention, as shown in Table 1, thickness: 10
A slab with a diameter of 0 mm and a width of 1200 mm was cast using an immersion nozzle with an outer diameter of 280 mm and an inner diameter of 50 mm while performing Ar plasma arc heating. Table 2 shows the electrical conditions of the plasma device employed at this time. That is, in the initial stage of casting, the temperature of the nozzle is low and heat is easily taken away, so the current value was set at a high value of 1200 A, and in the steady stage, this was reduced to 700 A to perform plasma arc heating.

In addition, as Comparative Example 1, a slab of the same size as above was used.
Casting was performed using nozzles of the same size and without plasma heating.

Furthermore, as Comparative Example 2, a slab of the same size was prepared with an outer diameter of 6
Casting was performed using a nozzle of 0+u, inner diameter: 30n without plasma heating.

Here, in the case of the present invention example and comparative example 1, the distance between the nozzle and the inner wall of the mold was approximately 10 m, and in the case of comparative example 2, the distance was approximately 2 m.
The casting speed was 2.5m/l1i in both cases.
It was set as n.

The casting conditions in the above test were observed, and the results are also shown in Table 1.

The following can be seen from the results shown in Table 1.

In the example of the present invention, stable casting is possible both in the early stage of casting and in the steady state, and a thin slab with good surface and internal quality can be obtained.

On the other hand, in Comparative Example 1, the nozzle broke at the early stage of casting, resulting in frequent casting stoppages. This was because the distance between the nozzle and the inner wall of the mold was as small as loN, and a solidified shell formed between them, and the nozzle was restrained by this. It is thought that stress was applied during the slab withdrawal and caused the breakage.

In Comparative Example 2, there were many situations in which hot water supply was insufficient during the process, forcing the drawing speed to be reduced, and situations in which the scene changed rapidly, but this was because the nozzle inner diameter was 3.
This is thought to be due to nozzle clogging due to the small size of 0 cranes.

From the above results, even if the slab thickness is as thin as 100 mm, if thermal compensation is performed by plasma heating as specified in the present invention, it will be stable even when using a large immersion nozzle with a nozzle outer diameter of 80 mm. 61 that casting is possible!
i = possible.

Summary of Effects> As explained above, according to the present invention, even in continuous casting using a rectangular mold with narrow long side spacing for thin-walled slab casting, stable work can be achieved by applying a large-diameter immersion nozzle. This brings about extremely useful effects industrially, such as making it possible to cast high-quality slabs under the same conditions.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating the continuous casting method according to the present invention. FIG. 2 is an explanatory diagram showing an example of a movement trajectory of a plasma arc spot to be irradiated. FIG. 3 is a schematic illustration of an argon plasma torch. Figure 4 is a drawing showing an example of a conventional mold for continuous casting of thin-walled slabs.
Figure (11) shows the A-A sectional view, and Figure 4 (C1 shows the BB sectional view. In the drawings, 1... Immersion nozzle, 2... Water-cooled copper mold. 3... Molten steel. , 4...Plasma torch 5
...Plasma arc 6...Dummy bar for drawing slabs 7...Solidified shell. 8... Movement trajectory of the plasma arc spot. 9...Water-cooled copper cylinder 11...Mold long side, 12...Transition surface. 13...Funnel-shaped pouring part.

Claims (1)

[Claims] A continuous casting method, characterized in that when performing continuous casting using an immersion nozzle, the molten metal between the immersion nozzle and the inner wall of the mold is cast while being heated with a plasma arc.