JPH02192854A - Method for controlling separating point in cast billet in twin directional drawing type horizontal continuous casting - Google Patents

Abstract

PURPOSE:To stabilize separating point of solidified shell in a cast billet and to maintain the above point at the fixed position near just below a feed nozzle by arranging spray cooling type nozzles at circumference of outer wall at center part of the mold, penetrating outer wall of the mold, slowly cooling mold copper plate at center part and forcedly cooling in accordance with apart from the center part. CONSTITUTION:In the inner part of the mold 6 at near just below the feed nozzle 8, the mold copper plate 6A is arranged and the inner part thereof is brought into contact with the molten steel 2 poured from the feed nozzle 8, and in the outside of the mold 6, the mold outer wall 6B consisting of iron shell is arranged. The plural atomizing nozzles 20 for cooling are fitted to upper and rear faces and both side faces of the outer wall 6B at center part of the mold. Each of the nozzle 20 for cooling provides a cooling water flow rate control valve 24 and a compressed air flow rate control valve 28, and the spraying flow rate can be independently controlled to each other. By this method, the separating point of the solidified shell in the cast billet is maintained to the fixed position and stable operation can be executed without any accident of breakout, etc., in the horizontal continuous casting.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling the separation point of slabs in bi-directional drawing type horizontal continuous casting, and in particular stabilizes the separation point position of both left and right solidified shells to improve the stability of casting. Regarding the slab separation point control method that can improve
Widely used in continuous steel casting field.

[Conventional technology]

In the field of continuous casting, instead of the conventional vertical or curved continuous casting method, a horizontal continuous casting method has been proposed in which a horizontally arranged continuous casting mold is used to pull out and cast slabs horizontally. Casting of slabs is carried out.

With these horizontal continuous casting methods, conventional vertical or curved continuous casting methods can be used to create buildings reaching heights of 30 to 40 meters,
This is attracting attention because of the advantages of being able to reduce the height of the building and having relatively low equipment costs, whereas the construction of a structure to support the large weight associated with this requires a large amount of cost.

The horizontal continuous casting method also changed from the initial method in which slabs were pulled out from the right end of the mold to a method in which slabs were pulled out from both ends of the mold in opposite directions, as disclosed in JP-A-58-138544. Improvements in production capacity have been achieved.

This method will be explained with reference to FIGS. 5(A) and 5(B).

Below a container 4, such as a ladle or a tundish, which accommodates molten steel 2, a mold 6 is horizontally arranged with its end facing in the horizontal direction. Container 4 and mold 6 are feed nozzle 8
This allows the molten steel 2 to communicate without leakage. Mold 6
consists of a mold copper plate 6A and a mold outer wall 6B. Mold 6
, the container 4 is vibrated left and right by a vibrating device 10, and the slab 12 in which the molten steel 2 has solidified is pulled out left and right by pinch rolls 1.4.

In horizontal continuous casting, in which slabs are drawn horizontally from both ends of the mold, it is necessary to satisfy the contradictory demands of forming a strong solidified shell without breakouts and stably breaking the solidified shell in a fixed position. be.

The formation of a solidified shell in a mold in horizontal continuous casting will be explained with reference to FIGS. 6(A), (B), and (C).

As shown in FIG. 6(A), the formation start position of the solidified shell 16 is located at the center of the mold 6, directly below the feed nozzle 8, and ideally the solidified shell 16 is broken at this point. However, in actual operation, for some reason, an unhealthy thin solidified shell 16 is formed in a portion away from the center as shown in FIG. 6(B) and breaks from there, and if this is repeated, the state shown in FIG. 6(C) occurs. As shown, a thin part of the solidified shell 16 with a large width is formed off the central part, and it breaks from there.Finally, the break position moves away from the mold 6 and a breakout occurs, resulting in a major accident. Also,
When the left and right solidified shells are separated in the thick part of the solidified shell,
Traces of the separation points remain as oscillation marks, but the thicker the solidified shell, the deeper the oscillation marks, which remain as flaws on the steel plate after rolling the slab, resulting in a problem of degrading the quality of the steel plate. .

In order to prevent the above-mentioned movement of the fracture position and to stably fracture the solidified shell at a fixed position, various studies have been made in the past. There is.

(a) A method of controlling the starting position of solidified shell formation using a highly insulating refractory.

(b) A method of controlling the starting position of solidified shell formation by applying localized slow cooling in the mold using a heater, refractory, or a combination thereof.

However, these methods have the following problems.

(A) When using refractories, it is difficult to match the surfaces of the refractories and the copper plate mold, and the refractories and copper plate molds are not only eroded during use, but also become uneven, causing breakouts. Additionally, the need to replace refractories increases running costs.

(B) When using a heater, the temperature of the copper plate of the mold increases, resulting in accelerated deformation and wear of the mold.

Other conventional techniques are as follows.

(c) A method of controlling the drawing speed of the left and right slabs so that the fracture position is located directly below the feed nozzle 8.

(d) In order to slowly cool the mold 6 near the feed nozzle 8, a method of plating or thermal spraying a material with low heat conductivity and conductivity on the mold copper plate 6A.

However, these methods also have the following problems.

(C) In method (c), the internal quality of the slab is unstable because the drawing speed of the left and right slabs is not constant.

(D) The method (d) has a small slow cooling effect and is expensive.

Therefore, the present inventors previously invented a method of applying ultrasonic vibration to the mold near the feed nozzle as a measure to stabilize the position of the separation point, and disclosed it in Japanese Patent Application No. 159610/1983. With this method, an air layer is created between the central mold copper plate near the feed nozzle and the solidified shell, which causes gradual cooling, and this area becomes the separation point, which has the effect of stabilizing the fracture position. However, it is still difficult to conclude that we have reached a level where we are fully satisfied. As a result, in actual operation, control is performed to stabilize the slab separation point at the center directly below the feed nozzle by changing the slab withdrawal speed of the left and right sections 1 and 2nd strand. .

However, the separation point control based on the difference in the drawing speed of the left and right slabs cannot be performed when the deviation direction of the separation point is opposite on the upper and lower surfaces and both side surfaces of the mold copper plate 6A, for example, when the separation point is If the separation point of surface D is deviated to the left side of the first strand, and the separation point of surface D is deviated to the right side of the second strand, the separation point control using the conventional slab drawing speed difference is as follows: All sides A,
B.C.

Since this method moves the separation point on the D plane in either the left or right direction, it is impossible to control such deviation to the normal position. As a result, the surface quality of the slab deteriorated.

[Problem that the invention seeks to solve]

An object of the present invention is to solve the problems of the prior art described above, and to transfer the solidified shell to the feed nozzle without using special refractories or heaters for the mold, and while keeping the drawing speed of the left and right strands the same. To provide a method for controlling the separation point of slabs in horizontal continuous casting of bi-directional drawing type, which separates at a fixed position directly below, prevents the occurrence of oscillation marks, and stably obtains slabs with good surface properties. be.

[Means for solving problems]

The gist of the present invention is as follows.

That is, in a bidirectional drawing type horizontal continuous casting method in which molten steel is injected from a ladle into a horizontally arranged mold through a feed nozzle and solidified slabs are pulled out from both ends of the mold in opposite directions, the central part of the mold is A plurality of spray cooling nozzles that can be independently controlled are provided around the outer wall of the mold, and the nozzles are arranged so that their tips penetrate the outer wall of the mold and face the mold copper plate, and a central mold surrounding the feed nozzle is provided. This is a method for controlling a slab separation point in horizontal continuous casting of a bidirectional drawing type, which is characterized by slowly cooling a copper plate and gradually cooling it strongly as it declines from the central part.

The details of the present invention will be explained with reference to FIG. FIG. 1 is a partial sectional view showing the continuous casting apparatus according to the present invention in the vicinity directly below the feed nozzle 8. A mold copper plate 6A is provided inside the mold 6, and its inner surface is in contact with the melt 112 injected from the feed nozzle 8, but in the conventional mold 6, a groove is provided inside the mold copper plate 6A to allow cooling water to flow. Feed nozzle 8
Directly below the feed nozzle, the flow rate of the cooling water is low and the cooling water is slowly cooled, and as it moves away from directly under the feed nozzle, the flow rate is gradually increased and the cooling water is strongly cooled. The present invention can be applied regardless of the structure of the conventional molded copper plate 6A. Therefore, it can be applied to conventional internal water-cooled molded copper plates as well as molded copper plates without internal water-cooled channels.

A mold outer wall 6B made of an iron shell is provided on the outside of the mold 6. As shown in FIGS. A plurality of spray cooling nozzles 20 are attached to the upper and lower surfaces A and B and both sides C5D, and as shown in FIG. It has a compressed air flow rate control valve 28 and is configured to be able to independently control the spray flow rate. Therefore, each spray cooling type nozzle 2o is connected to the mold outer wall 6B.
It penetrates through and is arranged so that its tip is perpendicularly opposed to the mold copper plate 6A. Therefore, the outer periphery of the central portion of the mold copper plate 6A is as shown in FIG.

A plurality of spray cooling nozzles 20 are provided in the length direction and width direction of the slab 16 to be formed.

The section where this spray cooling type nozzle 20 is provided varies depending on the cross-sectional size of the mold, but is usually 400 to 700 mn from directly below the feed nozzle 8 to the left and right.

[Effect]

Using the spray cooling device according to the present invention having the above configuration, molten steel 2
When injecting, from just below the feed nozzle 8 to the left and right 5
In the central part of the mold 6 within 0 mm, the spray cooling type nozzle 20 is adjusted to provide gentle cooling, and the sections from 50 to 400 m+ in the drawing direction from directly below the feed nozzle 8 are gradually provided with strong cooling. Spray cooling nozzle 2
The heat is removed from the mold copper plate 6A by mist spray from 0. In the present invention, slow cooling refers to the mold copper plate 6A.
It is assumed that there is heat removal of less than 1 OKcal/ff1in per 1d of surface of A, and strong cooling is defined as mold copper plate 6.
1,0~4,,OKcal/w per 1d of surface of A
Assume that there is heat removal of in.

The operation of the control method for controlling difficult spots in slabs according to the present invention will be explained with reference to FIGS. 3(A) and 3(B). In the mold copper plate 6A directly below the feed nozzle 8, the separation point 21 of the solidified shell 16 is
(A) As shown in the figure, if the 0-plane is deviated toward the left first strand, and the D-plane is deviated toward the right 2nd strand, the present invention can be applied to the 0-plane. For surface D, the first strand on the left side from the center point directly below the feed nozzle 8 is strongly cooled, the second strand on the right is slowly cooled, and the first strand on the left side is slowly cooled for surface D. By strongly cooling the right second strand side, the displacement of each strand is controlled, and the separation point 21 can be moved to the center directly below the feed nozzle 8 as shown in Figure (B).

〔Example〕

C: 0.04% Si: 0. O2 Mn: 0.45 Al2 0.020 Molten steel superheat degree △Tu: 20℃ 1
The present invention was applied to horizontal continuous casting using a mold of 50 nm x 150 mm, oscillation conditions of 150 cp top, and drawing speed of 2 m/mjn. That is, 50ffIll+ on each side from the center directly below the feed nozzle.
The section is slowly cooled, and the temperature is 400++n to the left and right from the center.
The position of 4,0 Kcal/mjn is strongly cooled to remove heat, and the middle part is the central part of 1,Q Kcal/wi.
The test was conducted by gradually increasing the amount of heat removed from n to 2,0 to 3,0 Kcal/min.

Although there was some deviation of the separation point 21 during the test, it was possible to adjust the separation point 21 using the method described above to restrain the separation point 21 at a fixed position approximately directly below the feed nozzle.

Oscillation marks and double skin were hardly observed in the slab after continuous casting was completed.

In addition, the difference in the amount of heat removed per 1 d of slab between the left first strand side and the right second strand side due to strong cooling and slow cooling measured during this test, and the separation point movement speed (+nm/m
1n), it was found that a relationship as shown in FIG. 4 existed.

[Effect of invention]

In the bidirectional drawing type horizontal continuous casting method, the most important technology is the control technology that stably maintains the separation point of the solidified shells of both the left and right strands at a fixed position directly below the feed nozzle.
With many conventional control techniques, it is impossible to control each side of the mold copper plate, making it extremely difficult to stably position the separation point. Spray cooling nozzles that can be controlled independently are installed in each of the nozzles, and the nozzles penetrate through the outer wall of the mold so that their tips face perpendicularly to the mold copper plate. The mold copper plate was controlled on a side-by-side basis by gradually cooling the mold more strongly as it left the mold, resulting in the following effects.

(a) The solidified slab solidified shell separation point could always be stably maintained at a fixed position directly below the feed nozzle.

(b) As a result of (a), there were no accidents such as breakouts in horizontal continuous casting, and stable operation was possible.

(c) Therefore, the manufactured slab has oscillation marks, 2
There were no defects such as heavy skin, and the surface quality was significantly improved.

(d) Productivity and yield were improved, and production costs were significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing a spray cooling device used in the nine point control method of the present invention, FIG. 2 is a schematic perspective view showing a molded copper plate equipped with a spray cooling type nozzle according to the present invention, and FIG. A
) and (B) are perspective views showing the movement of the separation point corresponding to each surface in a molded copper plate to explain the action and effect of the present invention, and FIG. 3(A) shows the movement of the separation point corresponding to each surface. Figure 3 (B) shows the normal separation point position on each surface controlled by the present invention, Figure 4 shows the position of the left first strand, which was found in the embodiment of the present invention. and right side,
Difference in heat removal per 1 d of slab on the second strand side (Kca
A diagram showing the relationship between the movement speed (mu/ff1in) of the slab separation point controlled by the present invention (mu/ff1in),
Figures 5(A) and 5(B) show a conventional bidirectional drawing type horizontal continuous casting device, and Figure 5(A) is a longitudinal cross-sectional view of the slab;
Figure 5 (B) is a sectional view in the width direction of the slab, Figures 6 (A) and (B).
) and (C) are cross-sectional views showing solidified shells and separation points in bi-directional drawing type horizontal continuous casting, where FIG. 6(A) is a normal state and FIG. 6(B) and (C) are an abnormal state. shows. 2... Molten steel 4... Container 6... Mold
6A... Mold copper plate 6B... Mold outer wall
8...Feed nozzle 12...Slab 1
6... Solidified shell 20... Spray cooling type nozzle

Claims (3)

[Claims] (1) In a bidirectional drawing type horizontal continuous casting method in which molten steel is injected from a ladle into a horizontally arranged mold through a feed nozzle and solidified slabs are pulled out from both ends of the mold in opposite directions, the mold A plurality of spray cooling nozzles that can be independently controlled are provided around the outer wall of the central part, and the nozzles are arranged so that they penetrate the outer wall of the mold and their tips face the mold copper plate, and the central part surrounding the feed nozzle is provided with a plurality of spray cooling nozzles that can be independently controlled. A method for controlling a slab separation point in bidirectional drawing type horizontal continuous casting, characterized by slowly cooling a mold copper plate and gradually cooling it strongly as it moves away from the central part. (2) In the slow cooling section of the central mold copper plate, heat is removed at a rate of 1.0 Kcal/min or less per 1 cm^2 of the surface of the copper plate, and in the strong cooling section away from the center, the heat is removed per 1 cm^2 of the copper plate surface. 1.0-4.0Kcal/mi
A method for controlling a slab separation point in bidirectional drawing type horizontal continuous casting according to claim (1), wherein n heat removal is performed. (3) The slow cooling section of the center mold copper plate extends from the center directly below the feed nozzle toward the drawing direction.
The strong cooling section of the mold copper plate is 5 mm or less from the center directly below the feed nozzle in the drawing direction.
A method for controlling a slab separation point in bidirectional drawing type horizontal continuous casting according to claim (1) or (2), wherein the separation point is set to 0 to 400 mm.