JPH03297542A - Twin roll type continuous casting method and intermediate vessel for pouring molten metal used for same - Google Patents

Abstract

PURPOSE:To improve the quality of strip surface by floating an intermediate vessel having a nozzle hole below the draft line on molten metal in pouring basin, continuously pouring the molten metal into the intermediate vessel and discharging the molten metal into the pouring basin from the nozzle hole. CONSTITUTION:The molten metal 2 poured into the pouring basin formed with cooling rolls 1a, 1b and side dams 3a, 3b, is continuously cast as the metal strip 4 through gap between the rolls 1a, 1b. Then, the intermediate vessel 6 having own weight capable of floating on the molten metal 2 and the nozzle hole at lower position of the draft line 7 is floated on the molten metal 2 in the pouring basin under condition of communicating the molten metal 2 in and out of the vessel 6. The molten metal is continuously poured into this floated intermediate vessel 6 from the nozzle 5 and the molten metal in the vessel 6 is discharged in the pouring basin from the nozzle hole. By this method, the development of uniform solidified shell is accelerated and the development of crack and fold in the strip can be prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a twin-roll continuous casting method for directly and continuously casting thin plates from molten metal (for example, molten steel) and an intermediate container for pouring the molten metal used therein. .

[Conventional technology]

The continuous thin sheet casting method, which directly produces thin sheets from molten metal, such as molten steel, has the advantages of omitting hot rolling, producing materials that are difficult to roll, and improving material properties due to the cold solidification effect.
This is a field that is undergoing significant development and many proposals have been made. Among these, in the twin roll method, coagulation occurs in the same way on both roll surfaces of a pair of rolls, so there is no bias in the solidification form, and both solidification shells formed on the roll surface in the process of passing through the closest point of the rolls are Because it is rolled down at the point closest to the rolls, porosity is unlikely to remain inside.1.The surface texture is relatively clean. For these reasons, development research is actively underway. Since this casting technology omits the hot rolling process, very strict requirements are placed on the quality of the cast thin plate.The quality of the thin plate surface is particularly important, and there are no problems such as wrinkles, cracks, and inclusion of impurities. Defects must be completely prevented.

In order to prevent the occurrence of such defects, it is important to equalize the temperature distribution and flow of the molten metal within the pool formed by the circumferential surfaces of the twin rolls. In particular, if there is a stagnant part of the molten metal flow on the surface of the pool, the temperature of the molten metal in that part will drop and the surface will solidify, or a scum of suspended oxides will form, and if this is rolled into the solidified shell by the rotating rolls, the surface of the thin plate will be This may cause defects. Furthermore, if the temperature of the molten metal in the pool is not uniform in the width direction of the thin plate, the surface temperature distribution of the thin plate will be uneven, which may cause cracks to occur during cooling.

Therefore, in the twin-roll continuous casting method, it is necessary to pour the molten metal so that the molten metal can be uniformly supplied to the entire pool and to suppress the temperature drop on the surface of the pool.

For this reason, conventionally, this type of pouring method
For example, in JP-A-64-5650.

It has been proposed to use a multi-hole nozzle to pour molten water horizontally onto the surface of the molten metal in order to equalize the temperature of the molten metal, and to also agitate the surface of the molten metal using the pouring method to prevent the surface temperature from decreasing. ing. Further, JP-A-62-21443 proposes electromagnetic stirring of the hot water surface with the aim of achieving the same effect.

[Problem that the invention seeks to solve]

The inventors conducted a horizontal pouring experiment as proposed above, but the height of the nozzle discharge port (immersion depth from the surface of the hot water)
This changes the behavior of the molten metal flow greatly. If the immersion depth from the molten metal surface is too deep, the effect of stirring the surface of the molten metal pool will be insufficient, and if the immersion depth is shallow, the discharge flow will cause ripples on the surface of the molten metal pool, which will prevent the slab from solidifying. It was found that uniformity is more likely to occur. on the other hand,
Although the level of hot water in the pool formed on the circumferential surface of the roll is controlled so that its height is approximately constant,
Some variation is inevitable depending on casting conditions.

The nozzles that have been proposed so far to obtain a discharge flow in the horizontal direction have their height position almost fixed even if the melt level changes, so when the melt level changes, the nozzle hole below the melt level Immersion depth varies. Therefore, it is difficult to keep the immersion depth of the nozzle hole stable and constant during casting. For this reason, the flow pattern of the discharged flow discharged into the pool behaves differently depending on the fluctuation of the hot water level, making it impossible to maintain a steady state. As a result, insufficient stirring and ripples occur irregularly, which also acts as a disturbance on casting control and causes problems in stable casting.

On the other hand, regarding the method of installing an electromagnetic stirring device above the water pool to stir the surface layer of the water pool, due to the structure of the device, it is necessary to cover almost the entire water pool, so it is difficult to combine it with a porous nozzle. Not only is this difficult, but the stirring effect also causes ripples on the surface of the pool, so overall, a satisfactory result cannot be obtained.

Therefore, an object of the present invention is to solve the problems of the prior art, to uniformly pour molten water over the entire bath without causing ripples on the surface of the bath, and to prevent a drop in temperature on the surface of the bath. It lies in the establishment of hot water technology.

[Failure to solve the problem]

The present invention aims to solve the above problem by keeping the position of the nozzle hole at a certain distance from the hot water level in the pool and moving up and down synchronously with the hot water level. The basic feature of the present invention is that the nozzle component is floated on the molten metal in the pool to make use of buoyancy in order to keep the immersion depth of the nozzle hole constant.

That is, according to the present invention, a pair of cooling rolls that rotate in opposite directions are arranged facing each other in parallel, and a pair of side dams in a direction perpendicular to the roll axis are provided to form a pool on the circumference of the pair of rolls. In the twin-roll continuous casting method, in which the molten metal is continuously injected into the pool space, and the molten metal in the pool is cooled on the circumferential surface of the rolls, a thin metal plate is continuously cast through the gap between the rolls. Floating an intermediate container on the molten metal in the pool, which has the weight to float on the molten metal in a state where the molten metal communicates with the inside and outside of the container, and has a nozzle hole at a position below the water line. A twin-roll continuous casting method has been devised which is characterized by continuously injecting molten metal into this floating intermediate container and discharging the molten metal in the container from the nozzle hole into the pool. At that time, multiple nozzle holes are provided in the side wall of the container, and the molten metal is discharged from the nozzle holes into the molten metal pool as a discharge stream with a slight upward slope in the horizontal direction, and when it reaches the vicinity of the molten metal surface. Preferably, the intermediate container is provided with means for horizontally changing its orientation.

The intermediate container (container-shaped float nozzle) to be used is a rectangular refractory made of refractory material that has a long side wall on the side facing the 100-circle circumferential surface of the twin rolls, a short side wall on the side facing the side dams on both sides, and a bottom. The container body may have a simple shape in which a plurality of nozzle holes are provided through the long and/or short side walls of the container body, and an opening serving as a molten metal receiving port is provided in the upper surface of the container body. At that time, if a floating plate (buffer wall) is installed that extends laterally from the outer peripheral surface of the floating plate, and the nozzle hole is passed through from the inside of the side wall at an angle toward the back surface of the floating plate, this floating plate can be Said means for horizontally redirecting the discharge flow.

In this way, the present invention, as a molten metal injection device for a twin-roll continuous caster, has a structure that performs height synchronization by itself on the surface of the molten metal pool using its buoyancy in response to fluctuations in the height of the molten metal surface in the pool. It is characterized by the use of an intermediate container with a nozzle hole, thereby solving the above-mentioned problems.

[Details of the invention] The content of the present invention will be specifically explained below with reference to the drawings.

FIG. 1 schematically shows the main parts of the equipment for carrying out the present invention, in which a pair of cooling rolls la + 1 b rotating in opposite directions are arranged facing each other with their axes parallel to each other,
A side dam 3a is formed so that a puddle 2 of molten metal is formed on the circumferential surface of the cooling rolls la and lb.

3b are arranged at both ends of the cooling rolls la and lb.

The molten metal 2 in the pool is cooled by the circumferential surfaces of the cooling rolls la, lb to form solidified shells 17a, 17b (FIG. 1) on the circumferential surfaces, and both solidified shells 17a, 17
When b passes through the narrowest part of cooling rolls la and lb, it is crimped and rolled into a continuous thin plate 4. Molten metal is continuously injected into the pool from an upper ladle, tundish, etc. (not shown) through an injection nozzle 5. In the present invention, injection from such an injection nozzle 5 is The flow is temporarily placed in the intermediate container 6. This intermediate container 6 is suspended in the molten metal 2 in the tundish, and even if the level of the molten metal in the tundish fluctuates during casting operation, the ejection line 7
remains almost constant relative to the water level. In addition, the floating intermediate container 6 is connected to support rods 8a and 8b that can be freely moved up and down so that it stays at a predetermined plane position within the pool. The support rods 8a, 8b are vertically expandable and retractable, but their positions are fixed in the lateral direction. The entire intermediate container 6, including the weight of the support rods 8a and 8b, floats on the molten metal 2 in the pool.

FIG. 2 shows a cross section of the center of the intermediate container in a direction perpendicular to the roll axis, and FIG. 3 shows a cross section of the center of the intermediate container in a direction parallel to the roll axis. As seen in these figures, the intermediate container 6 has long side walls 9a, 9b facing the circumferential surfaces of both the twin rows a and lb.

A short side wall 10a on the side opposite to both Zyde dams 3a and 3b,
10b, and has a rectangular shape with a square bottom 1], and nozzle holes 12 are formed in the long side walls 9a, 9b and the short side walls 10a, 10b. Further, on the - side of the intermediate container 6, a molten metal receiver is formed with a slot 3 for receiving the injection flow from the injection nozzle 5. A flange-shaped floating plate 14 extending laterally over the entire outer peripheral surface of the intermediate container 6 is integrally formed with the intermediate container. This floating plate 14 has a flat part on its back surface 15, and the entire intermediate container has its own weight such that the position of the back surface 15 of this floating plate 14 is equal to or slightly below the ejaculation line 7. ing. The material t of the intermediate container 6, which comes into contact with the injection flow from the nozzle 5 and the molten metal in the pool, is entirely made of refractory material.

FIG. 4 shows the shape of the lower half of the intermediate container shown in the direction of the TV-TV line arrow in FIGS. 2-3. As shown,
Long side walls 9a, 9b and short side walls 10a, 10 of the intermediate container
Nozzle holes 12 are formed in b, and these have a slit shape extending in the horizontal direction, and have an upward slope from the inner surface to the outer surface of each side wall.

FIG. 5 shows the relationship between the inclination of the upwardly inclined slit-shaped nozzle hole 12 and the floating plate 14.

As shown in the figure, the nozzle hole 12 has an inclination angle θ upward from the horizontal direction from the inside to the outside of the side wall.
A slit-like opening passage is formed inside the side wall. Then, a relationship is created such that the flat back surface 15 of the floating plate 4 exists on the imaginary line extending outward from the inclined nozzle hole 2.

The present inventors have determined the upward angle θ of the nozzle hole 12 and the floating plate 14.
Various model tests were conducted to determine the shape of the back surface 15 of the floating plate 14 when the upward angle θ is in the range of 30 to 45 degrees and the slit width of the nozzle hole 2 is d.
The distance d2 from the outer edge of the floating plate 14 to the point where it intersects with the virtual extension of the nozzle hole 12 is approximately 3xd1.
The discharge flow discharged into the water pool from the back surface 15 of the floating plate 14
It was confirmed that the molten metal could flow while changing direction horizontally, suppress ripples on the surface of the pool, and supply molten metal to the vicinity of the surface of the pool without stagnation. Therefore, the floating plate J4 functions as a buffer wall that buffers the pulsation of the discharge flow, and also functions as a deflection plate that changes the flow in the horizontal direction on the surface of the hot water. It is desirable to exist near the surface level.

The present inventors set the upward angle of the nozzle hole θ-450, the slit thickness d of the nozzle hole, = 5 mm, and the above d.
Using an intermediate container made of a zirconia refractory that satisfies the relationship 2 + d, molten stainless steel of 5IJS304 is cast with the width of the thin plate 4 - 1000 mm and the thickness - 2 m.
When carried out under the conditions of m, there were no ripples on the surface of the pool, and the molten metal flowed gently on both rolls], a
It was confirmed that the molten metal flowed toward 1b, and no peeling phenomenon was observed on the molten metal surface due to a decrease in the molten metal temperature.

The surface of the cast thin plate 4 was of good quality overall.

[Function and effect of the invention]

As described above, according to the present invention, the intermediate container 6 is floated on the molten metal 2 in the pool, and the molten metal is discharged from the nozzle hole 12 located below the weeping line 7 of the floating intermediate container 6. Since the molten metal is discharged into the pool, even if the level of the molten metal 2 in the pool changes below 1", there is no flow from the molten metal level to the nozzle hole 12.
The immersion depth remains constant. Therefore, if the position of the nozzle hole 12 is selected to be the most preferable position for the target casting equipment and operating conditions, the immersion position will always be maintained constant during casting regardless of fluctuations in the melt level. As a result, unlike conventional methods, there is an insufficient supply of molten metal near the molten metal surface due to variations in the immersion depth of the discharge port, insufficient stirring (when the discharge port becomes deep), and the occurrence of ripples (
Fluctuations in the flow pattern (such as when the discharge port becomes shallow) are prevented, and the quality of the thin plate surface is greatly improved.

Further, by providing the floating plate 14 integrally with the intermediate container 6, the positional relationship of the floating plate 14 with the hot water level is maintained unchanged even if the hot water level changes. The discharge flow discharged obliquely upward from the inclined nozzle hole 12 is buffered by the horizontal floating plate 14 and changes its flow in the horizontal direction while slowing down the flow velocity, so that the flow stagnates near the hot water surface. This also prevents the discharge flow from directly hitting the solidified shells 17a, 17b (FIG. 2) formed on the circumferential surface of the roll. Moreover, by arranging the nozzle holes 12 and the floating plates 14 on all sides of the intermediate container 6, it is possible to uniformly pour the molten metal into the entire pool.

As described above, it is possible to prevent the surface of the molten metal from peeling during casting, to prevent the surface of the molten metal from undulating, and to make the temperature distribution of the molten metal in the trough uniform.As a result, a uniform solidified shell 17a, The formation of 17b is promoted and the thin plate to be cast is prevented from cracking and from forming wrinkles.

[Brief explanation of drawings]

Fig. 1 is a perspective view of essential parts of a twin roll continuous casting machine for explaining the method of the present invention, Fig. 2 is a sectional view showing an example of an intermediate container according to the invention during casting, and Fig. 3 is a diagram of the intermediate container. FIG. 4 is a cutaway perspective view of the lower half of the intermediate container as viewed from the TV-IV arrow in FIGS. 2 and 3, and FIG. 5 is a cross-sectional view similar to FIG. FIG. 3 is a partial cross-sectional view showing the structure of the side wall of the intermediate container for explaining the relationship. la, lb...Cooling roll 2. Molten metal in the pool 3a, 3b...Side dam. 4. Thin plate to be cast 5. Injection nozzle into the intermediate container. 6. Intermediate container. 7...Liquid lines 8a, 8b...Support rod 9a that can be expanded and contracted in the vertical direction
, 9b...Long side walls 10a, 10b of the intermediate container...Short side wall 12 of the intermediate container...Nozzle hole 13...The molten metal receiver into the intermediate container is the inlet. 14. Floating plate (buffer wall). 15...Back side of floating board. 17a, 17b... Solidified shell on the circumferential surface of the roll.

Claims (6)

[Claims] (1) A pair of cooling rolls that rotate in opposite directions are disposed in parallel and facing each other, and at least a pair of side dams in a direction perpendicular to the roll axis are disposed on the circumference of the pair of rolls to form a pool, In the twin-roll continuous casting method, molten metal is continuously injected into the pool space, and while the molten metal in the pool is cooled on the circumferential surface of the rolls, metal sheets are continuously cast through the gap between the rolls. An intermediate container having a weight that allows it to float on the molten metal in a state in which the molten metal is in communication with the molten metal and having a nozzle hole at a position below the water line is floated on the molten metal in the pool, and this floating intermediate container is A twin-roll continuous casting method characterized by continuously injecting molten metal into a container and discharging the molten metal from the nozzle hole into the reservoir. (2) The twin-roll continuous casting method according to claim 1, wherein the discharge stream from the nozzle hole is discharged from the side wall of the container into the tundish basin with an upward slope rather than horizontally. (3) The twin-roll continuous casting system according to claim 1 or 2, wherein the discharge flow in the molten metal basin having an upward slope is directed horizontally by a floating plate existing near the molten metal surface in the molten metal basin. Law. (4) A refractory container body having a long side wall on the side opposite to both circumferential surfaces of the twin rolls and a short side wall on the side facing both side dams and a bottom, and the long side wall and/or the short side wall on the side opposite to both side dams. It consists of a nozzle hole that penetrates the side wall and a molten metal receiving port that opens on the top surface of the container body, and is used in twin-roll continuous casting machines whose entire dead weight is the weight that floats on the molten metal to be cast. Intermediate container for pouring molten metal. (5) The intermediate container for pouring molten metal according to claim 4, wherein the container body is provided with a floating plate projecting laterally from the outer peripheral surface of the container body. (6) The molten metal injection intermediate container according to claim 5, wherein the nozzle hole penetrates the side wall with an inclination in a direction from the inner side of the side wall below the back surface of the floating plate toward the back surface of the floating plate.