JPS6049839A - Supplying method of molten metal of twin belt caster - Google Patents

Abstract

PURPOSE:To produce stably and surely a thin billet which has a good surface skin and is free from nonmetallic inclusions by disposing a pouring nozzle having the width equal to the overall width of a casting mold into said mold apart at a space of a limited size from the inside surface of the mold and pouring a molten metal into the mold while maintaining the free surface of the molten metal into the mold within a tundish. CONSTITUTION:A pouring nozzle which is attached to a tundish 12 and is sized to the overall width of a casting mold is disposed on the upper stream side of the casting mold of a twin belt caster constituted of upper and lower belts 2, 2' and right and left dam blocks by having 2mm. space between the outside circumferential surface of said nozzle and the surfaces of the belts 2, 2' and the right and left dam blocks. A molten metal 5 is then poured into the mold while the free surface of the molten metal in the mold is maintained within the tundish 12. Then the need for using a lubricating agent between the nozzle 11 and the belts 2, 2' as well as the dam blocks is eliminated; moreover, the defective casting surface owing to fluctuation in the molten metal surface in the mold is prevented and the floatation of nonmetallic inclusions and oxidation of the molten metal surface in the tundish 12 are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for supplying molten metal when continuously casting thin metal slabs using a twin belt gear star.

In recent years, twin belt casters have been increasingly used for casting thin sheets of non-ferrous metals such as copper, lead, zinc, and aluminum because they can produce wide thin sheets from molten metal with high efficiency.

FIG. 1 is a schematic diagram of a conventional general twin belt caster in a cast state, with each of the upper and lower boots IJ-1, 1'
When molten metal 5 is injected from the molten metal supply device 4 disposed on the upper side of the mold into the mold that is continuously formed by the endless upper and lower belts 2.2' and the side dam blocks 3, which are moved by the rotation of the molten metal, the injected molten metal As the belt and the side dam block move, they are cooled and solidified by moving toward the lower side without creating a relative slip between them, so that the solidified slab 6 can be taken out continuously and easily at high speed. be.

Furthermore, recently there has been a growing trend to produce thin sheets directly from steel slabs by cold rolling without hot rolling, and it is now possible to cast wide and ultra-thin slabs at high speeds. Attempts have also been made to apply the twin-belt caster, which can be used to cast steel, to casting of steel.

By the way, in such a twin belt caster, it is necessary to uniformly inject molten metal into the gap between the upper and lower belts, which are wide and have an extremely narrow interval. A gutter or narrow nozzle, such as the one shown at 7 in (a) to (d), is indispensably used.

Figures 2 (a) and (b) show the molten metal supply gutter for supplying overflow to the molten metal surface in the mold in the state shown in Figure 1, and Figure 2 (e) shows the molten metal supply nozzle and the molten metal supply nozzle. 2
Diagram (d) is immersion? FIG. 3 is a schematic perspective view showing examples of box nozzles. The immersion box nozzle shown in FIG. 2(d) is placed so as to be immersed in the molten metal in the mold as shown in FIG. Although the molten metal is continuously supplied, essentially, the molten metal continuously supplied from a tundish or the like as shown by the reference numeral 8 in FIG. 2(a) is supplied by overflowing. This is the same as the molten metal supply gutter shown in (a) and (b).

However, the conventional hot water supply method using such a gutter or nozzle has the following problems, and it is difficult to obtain a product that satisfies these problems, especially when casting thin sheets of metal with a relatively high melting point. This was a major obstacle at the top.

That is, in overflow hot water supply using a gutter or immersion box nozzle as shown in Figures 2 (a), (b) and (d), the surface (free surface) of the molten metal in the O mold is injected by the overflow. The flow of molten metal tends to cause ripples,
This causes double skin, etc., and the surface skin of the obtained slab is more likely to deteriorate than that of conventional materials. Furthermore, extremely difficult control means are required to control the amount of hot water supplied and the hot water level to alleviate these inconveniences. ○ Since the hot water level exists within the mold of the twin belt caster, It is difficult to seal the molten metal, which tends to generate inclusions due to oxidation, and there is no time for non-metallic inclusions drawn in from water heating equipment such as O-tandy 5-thrush to float, and all of them are captured by the slab. In addition, when hot water is supplied using a hot water nozzle like the one shown in Figure 2 (C), the nozzle is likely to become clogged when applied to molten metal with a high melting point such as molten steel. There was this inconvenience.

From the above-mentioned viewpoints, the present inventors have determined that even when casting metals with high melting points such as steel, there will be no cause of deterioration of the surface skin of the slab, and there will be no cause of deterioration due to oxidation of the molten metal surface or entrainment from the tundish. Melting to twin belt casters that can minimize the inclusion of metal inclusions and ensure smooth work without worrying about nozzle clogging or other molten metal supply failures! (A) As shown in Fig. 4, the surface 10 of the molten metal 5 in the mold is lower than the surface of the hot water supply nozzle 11. If it is set so that it is located in the tundish 12 that follows the base, the level of the hot water can be easily controlled compared to when the hot water level exists inside the mold (
(Methods used in ordinary continuous casting machines can be applied as is.) In addition to significantly improving the surface of the cast slab, it is also easy to seal the surface of the molten metal, which reduces oxidation of the molten metal and eliminates interferences caught in from other sources. B) The surface of the molten metal 5 in the mold is raised to the tundish 12 as shown in Figure 4. In order to position the molten metal inside the mold, a molten metal supply nozzle with the full width of the mold is used as a molten metal supply device to inject the molten metal into the mold, which has a narrow gap. C) When arranging the hot water supply nozzle with the full width of the mold, twin belts consisting of upper and lower belts and left and right dam blocks are used. By leaving a gap of at most 2 mm between the inner surface of the mold of the caster and the outer circumferential surface of the nozzle, even when the belt or dam block rotates, the nozzle and these will come into contact and no friction will occur. In addition to eliminating the need for lubrication measures, the rotational movement of the belt and dam block causes the viscous molten metal to be drawn in the opposite direction from entering the gap, which prevents molten metal from leaking from the gap and prevents the molten metal from flowing. There is no need to wrap around the outer circumferential surface of the nozzle and form a free surface inside the mold.

Of course, the allowable range of this gap varies depending on the slab thickness, casting speed, type of molten metal, etc.
For example, in the case of molten steel, when moving the mold, ○ h > 60 mm, v (under the condition of 3 m/min: d < 21 nvLS Oh) 60 man + v > 3, ml ml
Under the condition of n: d (3 questions, Oh (60 questions, v (under the condition of 3TL/min: d
<4 mm.

Under the condition of Oh < 60 mm * v > 3 m/min: d (5 dragons) If the condition is satisfied, there will be no steel leakage [However,
h: Molten steel head (see Figure 4), v: Casting speed (m
/ m1n ) + d: @ Gap (mm) between the inner surface of the mold and the outer circumferential surface of the nozzle) Generally, if the gap is set to 2 mm or less, no leakage will occur regardless of the type of molten metal. D) Mold If a nozzle with full width dimensions is used, the nozzle hole can be elongated into a slit shape even if the nozzle thickness is small, so there is less chance of nozzle clogging, and therefore thin slabs of 100 mm or less can be easily manufactured. In fact, we have come to the knowledge shown in A) to D) above.

This invention was made based on the above findings,
When supplying molten metal to the twin belt caster, a gap of up to 2 mm is placed between the inner surface of the mold and the outer circumferential surface of the nozzle on the upper side of the mold of the twin belt caster, which consists of upper and lower belts and left and right dam blocks, so that the width of the mold can be adjusted. By arranging a full-width hot water supply nozzle and continuing hot water supply while maintaining the free surface of the molten metal in the tundish following the root of the hot water supply nozzle, a thin slab with good surface texture and high quality can be produced. It is characterized by stable production.

Note) The reason why the gap between the inner surface of the mold and the outer circumferential surface of the nozzle was limited to a maximum of 2 mm is because if the gap exceeds 2 μ, depending on conditions such as slab thickness, casting speed, or type of molten metal, This is because molten metal may leak.

FIG. 4 is a schematic perspective view of a main part showing a state in which molten metal is being supplied to a twin belt caster by the method of the present invention.

In FIG. 4, on the upper side of the mold of the twin belt caster, which is composed of upper and lower bells) 2.2' and left and right tom blocks (not shown), there is a hot water supply nozzle 11 with the full width of the mold attached to the tundish 12. However, its outer peripheral surface and
The upper and lower belts and the left and right dam block surfaces are arranged with a gap of 2 mm or less. Since the upper and lower belts and the dam block move, the mold-like molten metal 5 does not leak out from the gap due to the movement of the upper and lower belts and the dam block. Therefore, by adjusting the amount of molten metal in the tundish 12, the mold-like molten metal 5 can be easily removed. The surface is not exposed within the mold, but remains within the tundish, which communicates with the mold through the nozzle holes. When the hot water supply nozzle 11 is disposed on the twin belt caster through a minute gap in this manner and hot water is supplied while maintaining the free surface of the fin-shaped molten metal within the tundish 12, the hot water supply nozzle, belt and dam There is no need to use a lubricant between the block and the mold, and casting surface defects due to fluctuations in the mold surface are prevented.
Since it is possible to prevent the floating of non-metallic inclusions and the oxidation of the molten metal surface in the tundish, which is easy to seal, it is possible to stably cast high-quality thin slabs.

As a hot water supply nozzle, a nozzle with a penetrating nozzle hole can of course be used;
It is preferable to use a structure in which a crosspiece is provided at the outlet section for reinforcement, as shown in the schematic perspective view of the main part in the figure.

Further, as the material for the hot water supply nozzle, it is recommended to use fused silica in terms of spalling resistance and strength, and also because it can be integrally molded into a large size.

Next, the present invention will be explained by examples and in comparison with comparative examples.

Example A low-order aluminum guild having the chemical composition shown in Table 1 was produced by the method of the present invention in which an integrally molded fused silica hot water supply nozzle as shown in FIG. 5 was arranged on twin belt casters as shown in FIG. Copper was supplied to a twin belt caster to produce a thin slab having a slab thickness of 40 mm and a slab width of 600+at.

Table 1 The angle of inclination of the twin belt caster used at this time was 6° (i), the casting speed was 67717 ml ns, and the gap (d) between the inner surface of the mold and the outer surface of the nozzle was 2 fins.

Separately, for comparison, Figure 2 (c
) and a second nozzle with width: 500+nm.
Using the gutter shown in Figure (b), casting was carried out under the same conditions as in the examples of the present invention.

As a result, when a conventional nozzle was used, the nozzle became clogged approximately 10 minutes after IIJ was inserted, making it impossible to cast.

In addition, when conventional gutters were used, no particular problem occurred when casting strips, but it was very difficult to control the hot water level, and the surface texture in areas where the hot water level dropped became very bad. Ta. Furthermore, there were large slugs scattered about that were thought to be caused by inclusions from the tundish section.

In this way, in hot water supply using a gutter, areas with poor surface quality accounted for 10% of the total cast slab.

On the other hand, according to the hot water supply method according to the present invention, even though the gap between the mold and the nozzle was left open for 2 hours, there were no accidents such as inability to pour due to steel leakage, and stable pouring could be carried out. . Moreover, the surface quality of the obtained slab was extremely good, and there was no double skin in particular. Also, the number of slags is reduced by half compared to the conventional method using a gutter, and the level of inclusions in the slab is reduced to about 175 compared to the level of inclusions due to oxidation due to the elimination of oxidation at the surface of the mold. It was confirmed that there is.

When the cast slab obtained in the above 4 manner and applied with the method of the present invention was cold rolled, it was found that the reduction in surface flaws was particularly remarkable compared to a comparative ttK using a molten metal supply trough and a conventional nozzle.

As mentioned above, 1. According to the present invention, it is possible to stably and reliably produce a high-quality thin cast slab with good surface texture, less inclusion of non-metallic inclusions, and a slab thickness of 100 mm or less. Industrially useful effects are brought about, such as the ability to further reduce the manufacturing cost of metal sheet materials.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional general twin belt caster in a cast state, and Fig. 2 is a schematic perspective view showing an example of a conventional water heater. b), second
Figures (e) and 2 (d) show different examples, and Figure 3 is a schematic diagram showing the molten metal supply situation using the immersion box nozzle shown in Figure 2 (d). FIG. 4 is a schematic diagram showing the state of supplying molten metal to the twin belt caster in the method of the present invention, and FIG. 5 is a schematic perspective view of essential parts showing an example of four hot water supply nozzles used in the method of the present invention. In the drawing, 1... Upper pulley, 1'... Lower sea IJ+, 2...
...Upper belt, 2'...Lower belt, 3...Dam block, 4...Molten metal supply device, 5...Mold white metal molten metal, 6...Slab, 7...Mold supply device , 8.9.12... Tanditshu, 10... Hot water surface (free surface), 11... Hot water supply nozzle. Applicant Sumitomo Metal Industries Co., Ltd. Agent Kazuo Tomita and one other person Year 1 Figure 12 Figure 3 Year 4z

Claims (1)

[Claims] A hot water supply nozzle with the full width of the mold is placed on the upper side of the mold of a twin belt caster consisting of upper and lower belts and left and right dam blocks, with a maximum gap of 2 Nun between the inner surface of the mold and the outer circumferential surface of the nozzle. A method for supplying molten metal to a twin belt caster, characterized in that the free surface of the molten metal in the mold is held tightly in a tundish that follows the base of the molten metal supply nozzle while supplying the molten metal.