JP2020110814A - Scum weir, twin roll type continuous casting device, and method for producing thin slab - Google Patents

Abstract

To provide scum weirs capable of suppressing the generation of a ground metal in the surfaces of the scum weirs at least in the start of casting and stably performing casting, a twin roll type continuous casting device provided with the scum weirs, and a method for producing a thin slab.SOLUTION: A twin roll type continuous casting device has a process where a molten metal is fed to a molten metal pool part formed by a pair of rotating cooling rolls and a pair of side weirs via a molten metal nozzle, and a solidified shell is formed and grown at the circumferential face of each cooling roll to produce a thin slab. In the device, a scum weir 20 is arranged at the inside of the molten metal pool member so as to be confronted with the discharge port of the molten metal nozzle, and the molten metal pool part is provided with an electric heating part 22 of heating a molten metal immersion part 20a to be immersed into the molten metal.SELECTED DRAWING: Figure 5

Description

The present invention supplies molten metal to a molten metal pool portion formed by a pair of cooling rolls and a pair of side dams via a pouring nozzle to form and grow a solidified shell on the peripheral surface of the cooling roll. In a twin roll type continuous casting apparatus for producing a thin cast piece, a scum weir disposed in the molten metal pool section, a twin roll type continuous casting apparatus using this scum weir, and a method for manufacturing a thin cast piece is there.

As a method for producing a thin cast slab of metal, as shown in Patent Documents 1 and 2, for example, a pair of cooling rolls having a water cooling structure inside and rotating in opposite directions are provided, and a pair of rotating cooling rolls and a pair of cooling rolls are provided. The molten metal is supplied to the molten metal pool portion formed by the side weirs, the solidified shell is formed and grown on the peripheral surface of the cooling roll, and the solidified shells formed on the outer peripheral surfaces of the pair of cooling rolls are roll-kissed with each other. A twin-roll type continuous casting apparatus is provided which is pressed at points to produce a thin cast piece having a predetermined thickness.

In the twin roll type continuous casting device described above, when starting casting, a dummy sheet is inserted between the cooling rolls as shown in Patent Documents 1 and 2, and a pair of cooling rolls and a pair of side dams are provided. The molten metal is supplied to the molten metal pool portion formed by, and a thin cast piece is formed so as to be connected to the dummy sheet, and then the cooling roll is rotated to connect the dummy sheet and this dummy sheet from between the cooling rolls. It is designed to pull out thin cast pieces.

Here, in the above-mentioned molten metal pool portion, oxides and the like float above the molten metal pool portion to form a film-like foreign matter called scum, and this scum forms the circumferential surface of the cooling roll (details). Between the peripheral surface of the cooling roll and the solidified shell (hereinafter sometimes simply referred to as the peripheral surface of the cooling roll). The entrained scum causes uneven solidification and cooling of the thin cast piece, which causes surface cracks, surface defects, deterioration of the cast quality of the thin cast piece, and the like.
Therefore, there has been proposed a technique for suppressing the scum on the molten metal surface from being caught in the peripheral surface of the cooling roll when casting a thin cast piece using the twin roll type continuous casting device described above.

For example, Patent Document 3 discloses means for disposing a scum weir having a plate shape in the gap between the pouring nozzle and the cooling roll in the molten metal pool section to suppress the inclusion of scum.
The scum floated on the molten metal surface by immersing the scum weir between the pouring nozzle and the meniscus (the molten steel surface and the cooling roll contact start point, solidification start point) parallel to the axial direction of the cooling roll. Can be blocked. Since the molten metal reaches the meniscus through the lower part of the immersed scum weir, scum entrainment on the molten metal surface is largely prevented, and a sound cast piece is manufactured.

JP-A-63-224847 JP-A-07-232243 JP, 04-158959, A

By the way, when the casting is started and the molten metal is discharged from the pouring nozzle to the molten metal pool portion, the level of the molten metal surface gradually rises and the pouring nozzle and the scum weir are immersed in the molten metal. Generally, at the start of casting, the pouring nozzle is preheated, but the scum weir is not preheated. Since the scum weir is close to the cooling roll and the installation position must be accurate, it must be securely fixed to the frame surrounding the cooling roll, but it must be preheated at another place just before the start of casting. , Immediately before, it is difficult to fasten the frame. Therefore, the scum weir is fixed in advance at a predetermined position without being preheated.

Therefore, the molten steel discharged immediately after the start of casting has its molten metal surface gradually rising in the molten metal pool portion, and comes into contact with the unheated scum weir. Then, the temperature of the molten metal around the scum weir decreases, and the metal may adhere to the surface of the scum weir.
When this metal is caught during casting and causes a hot band, the slab is broken and the operation is stopped. Therefore, it is important for the stabilization of the casting start to prevent the molten steel temperature from lowering and the formation of metal by the scum weir.

The present invention has been made in view of the above situation, at least at the start of casting, the scum weir that can suppress the generation of metal on the surface of the scum weir and can perform stable casting, It is an object of the present invention to provide a twin roll type continuous casting apparatus equipped with a scum weir and a method for manufacturing a thin cast piece.

In order to solve the above problems, the scum weir according to the present invention supplies a molten metal through a pouring nozzle to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side weirs, In a twin roll type continuous casting apparatus for producing a thin cast piece by forming and growing a solidified shell on the peripheral surface of a cooling roll, the molten metal pool section is arranged so as to face the discharge port of the pouring nozzle. It is a scum weir that is provided with an electric heating unit that heats a molten metal immersion portion immersed in the molten metal in the molten metal pool portion.

According to the scum weir of this configuration, since the molten metal pool section is provided with the electric heating section for heating the molten metal dipping section immersed in the molten metal, the scum weir is immersed in the molten metal by the electric heating section. The molten metal immersion portion can be preheated, and it is possible to suppress the formation of a thick metal (1 mm or more in the present invention) on the surface of the scum weir. Even if the metal is attached to the surface of the scum weir, the metal is thinner than when it is not preheated. Therefore, the metal can be easily removed by the molten metal discharge flow from the pouring nozzle. Originally, the scum weir is arranged opposite to the discharge port of the pouring nozzle in order to block the discharge flow from the pouring nozzle so as not to directly transfer the scum to the cooling roll. Also for removal, it is necessary to dispose at a position facing the discharge port of the pouring nozzle.
Therefore, it is possible to prevent the thick metal from being caught in the solidified shell during casting, and to perform stable casting.

Here, in the scum weir of the present invention, it is preferable that the current-carrying heating section is made of a conductive refractory material.
In this case, since the electric heating section is made of a conductive refractory, the electric heating section can be formed as a part of the scum weir.
With this, the molten metal immersion portion of the weir main body can be accurately heated by the electric heating unit, and it is possible to further suppress the formation of a thick base metal on the surface of the scum weir.

In addition, in the scum weir of the present invention, an insulating refractory layer may be formed on at least the surface of the molten metal immersion portion.
In this case, since the insulating refractory layer is formed on the surface of the molten metal dipping portion, the current does not leak to the molten metal side even when electric heating is performed during casting, and the molten metal dipping is also performed during casting. It is possible to heat the part.

The twin roll type continuous casting apparatus of the present invention supplies molten metal through a pouring nozzle to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and a peripheral surface of the cooling roll. A twin-roll type continuous casting apparatus for producing and growing a solidified shell to form a thin cast piece, wherein the scum weir described above faces the discharge port of the pouring nozzle in the molten metal pool section. It is characterized by being arranged.

According to the twin roll type continuous casting apparatus having this configuration, the scum weir described above is disposed in the molten metal pool portion so as to face the discharge port of the pouring nozzle, so that when casting is started, etc. Therefore, it is possible to suppress the formation of metal on the surface of the scum weir, and it is possible to stably start the casting. Further, it is possible to suppress the scum from being caught in the solidified shell, and it is possible to manufacture a high-quality thin cast piece.

The method for manufacturing a thin cast product of the present invention is to supply a molten metal through a pouring nozzle to a molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams, and a peripheral surface of the cooling roll. A method of manufacturing a thin cast product for forming and growing a solidified shell on a thin cast product, wherein the scum weir described above is disposed in the molten metal pool portion so as to face the discharge port of the pouring nozzle. It is characterized in that the molten metal immersion portion of the weir body is heated by the electric heating portion at least before the start of casting.

According to the method for manufacturing a thin cast slab of this configuration, since the scum weir described above is arranged in the molten metal pool portion so as to face the discharge port of the pouring nozzle, the scum becomes solidified shell. Entrainment can be suppressed and high quality thin cast pieces can be manufactured.
Further, at least before the start of casting, since the molten metal immersion portion of the weir body is heated by the current-carrying heating unit, it is possible to suppress the formation of metal on the surface of the scum weir at the start of casting, etc. It is possible to start stably.

Here, in the method for manufacturing a thin cast product of the present invention, the molten metal is molten steel, and the surface temperature Tsf of the molten metal dipping portion is controlled by the energizing heating portion so as to satisfy the following equation. It is preferable to heat.
Tsf≧TL−0.7×(TL−TS)−0.92×(ΔTm+0.7×(304+TL−TS))
TL: liquidus temperature, TS: solidus temperature, ΔTm: superheat in molten metal pool part

In this case, since the molten metal is molten steel and the surface temperature Tsf of the molten metal soaked portion is heated by the electric heating unit so as to satisfy the above formula, it is formed on the surface of the scum weir. It is possible to suppress an increase in the solid fraction of the metal, and it is possible to easily remove the metal by the molten steel discharge flow from the pouring nozzle. Therefore, it is possible to more accurately suppress the involvement of the metal.

As described above, according to the present invention, at least at the start of casting, it is possible to suppress the generation of metal on the surface of the scum weir, and to perform stable casting, and a scum weir equipped with this scum weir. It is possible to provide a roll-type continuous casting device and a method for manufacturing a thin cast piece.

It is an explanatory view showing an example of a twin roll type continuous casting device which is an embodiment of the present invention. It is a partially expanded explanatory view of the twin roll type continuous casting apparatus shown in FIG. It is sectional explanatory drawing of the molten steel pool part of the twin roll type continuous casting apparatus shown in FIG. It is an upper surface explanatory view of the molten steel pool part shown in FIG. It is explanatory drawing of the scum weir which is embodiment of this invention. (A) is a front view and (b) is a side view. It is explanatory drawing which shows various structures of the scum weir which is embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following embodiments, the target metal to be cast will be described as steel. The present invention is not limited to the embodiments below.

In the present embodiment, molten steel is used as the molten metal, and the thin cast piece 1 made of steel material is manufactured. As the steel type, for example, 0.001 to 0.01% C ultra low carbon steel, 0.01 to 0.10% C low carbon steel, 0.10 to 0.4% C medium carbon steel, 0.4 -1.2% C high carbon steel, austenitic stainless steel typified by SUS304 steel, ferritic stainless steel typified by SUS430 steel, 3.0-3.5% Si directional electromagnetic steel, 0.1 6.5% Si non-oriented electrical steel and the like (where% is% by mass) can be mentioned.
Further, in the present embodiment, the width of the thin cast piece 1 to be manufactured is within the range of 200 mm or more and 1800 mm or less, and the thickness is within the range of 0.8 mm or more and 5 mm or less.

A twin roll type continuous casting apparatus 10 used in the method for manufacturing a thin cast piece according to the present embodiment will be described.
The twin roll type continuous casting apparatus 10 shown in FIG. 1 includes a pair of cooling rolls 11, 11, pinch rolls 12, 12 and 13, 13 for supporting the thin cast piece 1, and a width direction of the pair of cooling rolls 11, 11. A side weir 15 disposed at an end, a tundish 18 for holding the molten steel 3 supplied to a molten steel pool portion 16 defined by the pair of cooling rolls 11, 11 and the side weir 15, and this tank A pouring nozzle 19 for supplying the molten steel 3 from the dish 18 to the molten steel pool portion 16 is provided.

Here, as shown in FIG. 3, molten steel 3 is stored in the molten steel pool portion 16, and a scum X made of an alumina film or the like is formed on the molten steel surface.
In order to prevent the scum X from being caught in the cooling roll 11, a scum weir 20 is provided in the molten steel pool portion 16. More specifically, as shown in FIGS. 2 to 4, the scum weir 20 has a rectangular flat plate shape and is arranged between the pouring nozzle 19 and the cooling rolls 11, 11 and a part of the molten steel 3 It is immersed inside.

FIG. 5 shows an example of the scum weir 20 according to the present embodiment. The scum weir 20 shown in FIG. 5 includes a weir main body 21 and an electric heating portion 22 that heats the molten steel dipping portion 20 a that is dipped in the molten steel 3.
The molten steel immersion portion 20a is a region in the molten steel pool portion 16 that is immersed in the molten steel 3, and may be defined from the previously assumed immersion depth D of the scum weir 20.
The weir body 21 is made of a material that has strength and heat resistance and is less likely to be thermally deformed. Specifically, oxides such as alumina and zirconia, boron nitride, aluminum nitride, nitrides such as silicon nitride, graphite, and composite materials thereof can be used. For example, alumina graphite (AG) is widely used because it is easily available.

The electric heating section 22 is made of a conductive material, and is configured to heat the molten steel dipping section 20a by Joule heat generated by energizing the electric heating section 22.
In addition, in the scum weir 20 which is this embodiment, the electric heating part 22 is, for example, alumina graphite (for example, C content is 10 to 30 mass%), zirconia graphite (for example, C content is 10 to 40 mass%). , ZrB ₂ -C (for example, the C content is 0 to 95 mass%) and the like.

Here, the structure of the scum weir 20 according to the present embodiment is not limited to that shown in FIG. Various structures of the scum weir 20 will be described with reference to FIG. In FIG. 6, the unhatched part is the weir body 21, and the hatched part is the electric heating part 22.
First, in FIG. 6, the scum weir 20 is classified into the following four types of A type, B type, C type, and D type depending on the location where the electric heating section 22 is provided.
A type: Structure in which electric current heating part 22 is arranged in molten steel immersion part 20a B type: Structure in which electric current heating part 22 is arranged above molten steel immersion part 20a C type: Electric current heating part 22 is provided on the entire surface of scum weir 20 Arranged structure D type: Structure in which an electric heating unit 22 is arranged at both ends in the width direction of the scum weir 20.

Further, in FIG. 6, the scum weir 20 is classified into the following four types of type I, type II, type III, and type IV according to the arrangement method of the electric heating unit 22.
Type I: An electric heating unit 22 is arranged on one surface side of the scum weir 20.
Type II: An electric heating unit 22 is arranged in the entire thickness direction of the scum weir 20.
Type III: Energized heating part 22 (or weir body 21) is sandwiched from both ends in the width direction
Type IV: An electric heating unit 22 is placed on one surface of the weir body 21.

Here, in the A type having a structure in which the electric heating section 22 is provided in the molten steel dipping portion 20a, when energized while being immersed in the molten steel 3, the energized electricity will leak to the molten steel 3 side. .. For this reason, it is preferable to energize and heat the energization heating unit 22 before the start of casting.
In addition, when an insulating refractory layer is formed on the surface of the molten steel immersion part 20a, it becomes possible to heat by energizing during casting.

Further, in the B type having a structure in which the electric heating section 22 is disposed above the molten steel dipping section 20a, the electric heating section 22 is not immersed in the molten steel 3, so that the electric heating is performed even before casting and during casting. It becomes possible to energize the portion 22 to heat it. In addition, in order to heat the molten steel immersion portion 20a by heat conduction without directly heating it, it is necessary to increase the amount of heat generated in the electric heating portion 22.

In the C-type having the structure in which the electric heating section 22 is disposed on the entire surface of the scum weir 20, the entire scum weir 20 can be efficiently heated.
Also in this C-type, since the electric heating section 22 is also provided in the molten steel dipping section 20a, it is preferable that the electric heating section 22 is energized and heated before the start of casting.
Further, when the insulating refractory layer is formed on the surface of the molten steel dipping portion 20a, it becomes possible to heat by applying electricity during casting.

In the D type having a structure in which the electric heating portions 22 are arranged at both ends of the scum weir 20 in the width direction, the scum weir 20 can be efficiently heated in the vicinity of the side weir 15 where molten steel flow tends to stagnant. It is possible to suppress the generation of metal.
Also in this D type, since the electric heating section 22 is also provided in the molten steel immersion section 20a, it is preferable to apply electric current to the electric heating section 22 to heat it before the start of casting.
Further, when the insulating refractory layer is formed on the surface of the molten steel dipping portion 20a, it becomes possible to heat by applying electricity during casting.

In the I type in which the electric heating section 22 is arranged on one surface side of the scum weir 20, the surface on the side where the electric heating section 22 is arranged is efficiently heated. Here, since the surface of the side facing the pouring nozzle 19 is heated by the molten steel flow from the pouring nozzle 19, in the case of the I type, one surface on which the electric heating section 22 is arranged is a cooling roll. It is preferable to install the scum weir 20 so as to face the 11 side. Here, the weir main body 21 and the electric heating section 22 are joined together by using an adhesive or the like.
The scum weir 20 shown in FIG. 5 corresponds to type A and type I.

In the type II in which the electric heating section 22 is arranged in the entire thickness direction of the scum weir 20, both surfaces of the scum weir 20 can be efficiently heated.
Here, the weir main body 21 and the electric heating section 22 are joined together by using an adhesive or the like.
In addition, in the C type II type, the entire scum weir 20 is composed of the electric heating section 22.

In the III type having a structure in which the energization heating section 22 (or the weir main body 21) is sandwiched from both ends in the width direction, the energization heating section 22 can be fixed at a predetermined position.
In addition, in the D type III type, the weir main body 21 is sandwiched and fixed by the electric heating section 22.

In the IV type having a structure in which the electric heating unit 22 is placed on one surface of the weir main body 21, it is not necessary to process the weir main body 21, so the electric heating unit 22 can be arranged relatively easily. Becomes However, since the unevenness is formed on the surface of the scum weir 20 or the thickness of the scum weir 20 itself becomes thick, it is necessary to handle it with caution.

As described above, the installation position and method of the energization heating unit 22 should be appropriately selected in consideration of the temperature rising efficiency, manufacturability, manufacturing cost, easiness of energization to the energization heating unit 22, and the like. Is preferred.

In order to energize the energization heating unit 22, energization electrodes to which a power cable is connected are provided at two locations of the energization heating unit 22, generally on both sides in the width direction. For the electrodes, a material having low electric resistance and excellent heat resistance and thermal shock resistance, such as graphite or ZrB ₂ -C (C: 0 to 95 mass %), can be used.
The method for disposing the electrodes on the electric heating section 22 (conductive refractory material) is not particularly specified, but (a) the electrode is pressed against the electric heating section 22 for pressure bonding, or (b) the electrode (graphite electrode, etc., a processable material). No. 1) is screwed, a screw hole is formed in the electric heating section 22, and both are screwed together, or (c) a heat-resistant adhesive having low electric resistance is used for bonding. Power is supplied from a power panel installed on the machine side of the twin roll continuous casting machine 10 through a power cable.

Next, a method for manufacturing the thin cast piece 1 by the twin roll type continuous casting apparatus 10 including the scum weir 20 according to the present embodiment will be described.

In the twin roll type continuous casting apparatus 10, as shown in FIGS. 1 to 4, the scum weir 20 described above is arranged in the molten steel pool portion 16 so as to face the discharge port of the pouring nozzle 19. .. That is, the scum weir 20 is arranged at a position corresponding to the width of the discharge port of the pouring nozzle 19. The width of the discharge port is the width of the discharge port if the discharge port is single on one side.If the discharge port is composed of multiple discharge ports on one side, all the discharge ports on one side are included. It is the width and length of the entire area. Arranging the scum weir 20 at a position facing the discharge port has the above meaning.
The immersion depth D of the scum weir 20 is preferably 3 mm or more. Further, as shown in FIG. 4, the scum weir 20 is preferably arranged so as to extend parallel to the rotation axis of the cooling roll 11.
This can prevent the scum X from being directly caught between the cooling roll 11 and the solidification shell 5.

In this twin roll type continuous casting apparatus 10, the molten steel 3 is brought into contact with the rotating cooling rolls 11 and to be cooled, so that the solidified shells 5 and 5 grow on the peripheral surfaces of the cooling rolls 11 and 11. The solidified shells 5, 5 formed on the pair of cooling rolls 11, 11 are pressed against each other at the roll kiss points to cast the thin cast piece 1 having a predetermined thickness.

In the present embodiment, at least before the start of casting, in the scum weir 20, the molten steel immersion part 20a is heated by the electric heating part 22.
Then, in the present embodiment, it is preferable that the electric current heating unit 22 heats the molten steel soaked portion 20a so that the surface temperature Tsf satisfies the following expression (1).
Formula (1): Tsf≧TL−0.7×(TL−TS)−0.92×(ΔTm+0.7×(304+TL−TS))
TL: liquidus temperature, TS: solidus temperature, ΔTm: superheat in molten steel pool

The above formula (1) will be described below.
Consider a case where molten steel 3 comes into contact with the surface of the scum weir 20, is cooled, solidification proceeds, and metal is produced. The molten steel 3 contacting the surface of the scum weir 20 starts solidification at the liquidus temperature TL and completes solidification at the solidus temperature TS. The temperature range from the liquidus temperature TL to the solidus temperature TS is a solid-liquid coexistence region, and the solid phase ratio increases as the temperature decreases.

In the tissue morphology in the solid-liquid coexistence range during solidification, the solid phase ratio is 0.3 or more, and adjacent solid phases (generally dendrite tissues) start to be connected. When the solid phase ratio is in the range of 0.3 or more and 0.7 or less, the liquid phase between the solid phases can flow and the bonding between the solid phases is weak. Therefore, the metal in this state can be easily separated from the surface of the scum weir 20 due to the flow of the molten steel 3. On the other hand, when the solid phase rate exceeds 0.7 and the solidification proceeds, the bonding between the solid phases proceeds, and the liquid phase is confined between the solid phases and distributed in an isolated form. In such a form, it is difficult to separate the metal from the surface of the scum weir 20 because the solid phase bond is firm.

Therefore, in order to easily separate the metal from the surface of the scum weir 20, the bond between the solid phases should be relatively weak, that is, the solid fraction should be 0.7 or less, that is, the surface temperature of the molten steel dipping portion 20a. It is effective not to set Tsf to a temperature below the solid phase ratio of 0.7.
Therefore, at the start of casting, the molten steel 3 that has come into contact with the scum weir 20 and cooled is heated by the electric heating unit 22 so that the solid fraction is 0.7 or less, and the surface temperature Tsf of the molten steel immersion unit 20a is increased. Secure.

First, the amount of heat (enthalpy) required for the molten steel 3 to solidify will be described. In order for molten steel 3 to solidify,
(A) Amount of heat sufficient to cool the molten steel superheat ΔTm and reduce it to the liquidus temperature TL;
(B) Latent heat of solidification 60 kcal/kg,
(C) A heat quantity corresponding to the temperature difference (solidification temperature range) of TL-TS,
It is necessary to remove the total amount of heat.

The amount of heat is enthalpy, and the enthalpy per unit weight of (a) and (c) is a value obtained by multiplying the specific heat of molten steel 0.197 kcal/kg/K by the temperature change. That is, the enthalpy of (a): H(a)=0.197×ΔTm, and the enthalpy of (c): H(c)=0.197×(TL-TS). Further, the solidification latent heat L (enthalpy) of pure iron is 60 kcal/kg, and when converted using the specific heat of the molten steel 3, the solidification latent heat corresponds to a temperature change of the molten steel 3 of 304°C. Therefore, it is displayed in the same format as H(a) and H(c), and is approximated by H(b)=0.197×304.
The enthalpy change when increasing from the solid phase ratio=0 (liquidus temperature TL) to the solid phase ratio of 0.7 is 70% of the total of H(b) and H(c). In practice, the surface temperature Tsf of the molten steel immersion portion 20a of the scum weir 20 can be easily controlled by displaying the temperature. Therefore, the enthalpy is divided by the specific heat to be converted into a temperature change.

Next, the thermal energy balance when the molten steel 3 having the superheat degree ΔTm comes into contact with the surface of the scum weir 20 at a temperature lower than the molten steel temperature and is deheated is calculated. As a premise, between the refractory material of the scum weir 20 (thickness is generally about 5 to 15 mm, often 10 mm) and the molten steel 3 in contact with the scum weir 20 of the same thickness (the width is the same, so the volume is the same). The thermal energy balance of is assumed. Generally, the thickness of the metal attached to the scum weir 20 is 5 mm or less on one side and 10 mm or less on both sides in total, so the above assumption is appropriate.

Here, the thermal conductivity λ of the refractory of the scum weir 20 is lower than that of the molten steel 3 and is about ½ or less. Since the penetration depth δ of the temperature distribution in the thickness direction of the scum weir is proportional to √λ, the penetration depth of the temperature distribution in the refractory of the scum weir 20 is 1/√2≈0.71 of molten steel. Therefore, in the calculation of the thermal energy balance, it is sufficient to consider 0.71 times the refractory thickness from the surface layer of the scum weir 20.

In the calculation below, the temperature distribution inside the scum weir is assumed to be constant. In reality, the temperature becomes higher toward the surface layer due to the heat conduction of the refractory material of the scum weir 20, and this assumption is a strict condition under which the molten steel 3 is cooled more strongly than in reality.
Since the specific heat (kcal/kg/K) of the refractory used for the scum weir 20 is alumina graphite (AG): about 0.3, BN: 0.31, ZrO ₂ : 0.14, etc. 3 kcal/kg/K is considered a representative value.

When the molten steel immersion portion 20a of the scum weir 20 receives thermal energy from the molten steel 3 and the temperature rises by ΔT(R), the enthalpy received by the refractory material of the scum weir 20 is expressed by equation (2).
Formula (2): H(R)=0.3×ΔT(R)×0.71
The last value 0.71 considers the penetration depth of the temperature distribution.

If the temperature of the molten steel immersion portion 20a after receiving H(R) rises to a temperature T(0.7) which is the solid fraction of the cast steel type of 0.7 or higher, it adheres to the surface of the scum weir 20. The temperature of the metal does not fall below T(0.7).
Therefore, if the surface temperature Tsf of the molten steel immersion portion 20a of the scum weir 20 is preheated to T(0.7)−ΔT(R) or more, the adhered metal can be easily peeled off.
Formula (3): Tsf≧T(0.7)−ΔT(R)

Next, ΔT(R) is calculated. Thermal energy is transferred from the molten steel 3 to the refractory, and the temperature is lowered from TL+ΔTm to the temperature T(0.7) at which the solid fraction is 0.7. T(0.7) is expressed by the following equation (4).
Formula (4): T(0.7)=TL-0.7×(TL-TS)

The enthalpy change in this case is expressed by the equation (5).
Formula (5): 0.197×ΔTm+0.7×{H(b)+H(c)}
=0.197×[ΔTm+0.7×{304+(TL-TS)}]

Since the expressions (2) and (5) are the same, ΔT(R) is expressed by the expression (6).
Formula (6): ΔT(R)=(0.197/0.3/0.71)×[ΔTm+0.7×{304+(TL-TS)}]

By substituting the equations (4) and (6) into the equation (3), the above equation (1) is obtained.
Formula (1): Tsf≧TL−0.7×(TL−TS)−0.92×(ΔTm+0.7×(304+TL−TS))

As described above, the formula (1) is a condition for suppressing the solid fraction of the adhered metal to 0.7 or less in consideration of the solidification latent heat discharged when the metal is generated on the surface of the scum weir 20. Is a formula that defines. Since the solid fraction of the adhered metal can be 0.7 or less, the discharge flow of the pouring nozzle 19 can easily separate the metal from the surface of the scum weir 20.
Since the scum weir 20 is arranged at a position facing the discharge port of the pouring nozzle 19, in order to prevent the scum X from being directly caught in the solidification shell 5, the scum X is discharged from the pouring nozzle 19. The flow can be used effectively. That is, when the discharge flow hits the scum weir 20, the thermal energy of the discharge flow raises the temperature of the adherent metal, which facilitates melting and facilitates separation from the surface of the scum weir 20. Further, the kinetic energy of the discharge flow facilitates mechanical separation from the surface of the scum weir 20. The present invention is constructed in consideration of these two effects.

When the solid fraction of the metal adhered to the surface of the scum weir 20 is set to 0.5 or less, the surface temperature Tsf of the molten steel dipping portion 20a is set so that the surface temperature Tsf satisfies the following equation (11). It is preferable to heat by the heating unit 22.
Formula (11): Tsf≧TL−0.5×(TL-TS)−0.92×(ΔTm+0.5×(304+TL-TS))

Further, when the solid fraction of the metal adhered to the surface of the scum weir 20 is set to 0.3 or less, the surface temperature Tsf of the molten steel dipping portion 20a satisfies the following equation (21) so that the electric current is applied. It is preferable to heat by the heating unit 22.
Formula (21): Tsf≧TL−0.3×(TL-TS)−0.92×(ΔTm+0.3×(304+TL-TS))

In order to manage the surface temperature Tsf of the molten steel immersion portion 20a, a thermocouple may be attached to the molten steel immersion portion 20a to measure the temperature. Further, the surface temperature may be controlled by attaching a thermocouple to a portion near the molten steel immersion portion 20a, which is not directly immersed in the molten steel 3. In this case, if the temperature difference between the thermocouple mounting position and the molten steel immersion portion 20a is measured in advance, the surface temperature of the molten steel immersion portion 20a can be grasped. Alternatively, a radiation thermometer may be used for non-contact temperature measurement, and any temperature measurement means may be used. Further, if there is a temperature distribution in the width direction of the scum weir 20, heating may be performed so that the surface temperature of the lowest temperature portion where the metal is likely to adhere satisfies the formula (1).

In the scum weir 20 according to the present embodiment having the above-described configuration, the molten steel immersion portion 20a can be preheated by the electric heating portion 22, and it is possible to suppress the formation of a thick base metal on the surface of the scum weir 20. .. Moreover, since the metal is not firmly attached, the metal can be easily removed by the discharge flow of the molten steel 3 from the pouring nozzle 19.
Therefore, the thick metal can be prevented from being caught in the solidified shell 5 during casting, and stable casting can be performed.

Further, in the present embodiment, since the electric heating section 22 is made of a conductive refractory material, it can be integrally formed with the weir body 21 made of a refractory material. Further, the electrification heating section 22 can be configured by configuring at least a part of the weir main body 21 with a conductive refractory material. Further, the entire scum weir 20 may be made of a conductive refractory material to serve as the electric heating section 22.
Therefore, the molten steel immersion part 20a can be accurately heated by the electric heating part 22, and it is possible to further suppress the formation of a thick base metal on the surface of the scum weir 20.

Further, in the scum weir 20 of the present embodiment, when an insulating refractory layer is formed on at least the surface of the molten steel dipping portion 20a, current may leak to the molten steel 3 side even if electric heating is performed during casting. Therefore, it is possible to heat the molten steel dipping portion 20a by energizing the electric heating portion even during casting.

Further, in the present embodiment, since the scum weir 20 described above is arranged in the molten steel pool portion 16 so as to face the discharge port of the pouring nozzle 19, the scum weir 20 is provided at the start of casting or the like. It is possible to suppress the formation of metal on the surface of the, and to start casting stably. Further, the scum X can be suppressed from being caught in the solidified shell 5, and the high quality thin cast piece 1 can be manufactured.

Further, in the present embodiment, when the surface temperature Tsf of the molten steel immersion part 20a is heated by the electric heating part 22 so as to satisfy the above-mentioned formula (1), the base metal generated on the surface of the scum weir 20. The solid phase ratio of can be 0.7 or less. In this way, by lowering the solid fraction of the metal generated on the surface of the scum weir 20, the metal can be easily separated by the molten steel flow from the pouring nozzle 19, and the metal grows thick. Can be suppressed. Therefore, it is possible to more accurately suppress the involvement of the metal.

Although the scum weir, the twin roll type continuous casting apparatus and the method for manufacturing a thin cast piece which are the embodiments of the present invention have been specifically described above, the present invention is not limited thereto, and the technical aspects of the invention are not limited thereto. It can be appropriately changed without departing from the idea.
For example, in the present embodiment, as shown in FIG. 1, the twin roll type continuous casting apparatus in which the pinch rolls are arranged has been described as an example, but the arrangement of these rolls is not limited, and the design may be changed appropriately. May be.

Below, the result of an experiment conducted to confirm the effect of the present invention will be described.

C: 0.08 mass%, Si: 0.6 mass%, Mn: 2.2 mass%, P: 0.01 mass%, S: 0.005 mass%, Al: 0.03 mass% A thin cast piece made of carbon steel was manufactured using the twin roll type continuous casting apparatus shown in the above-mentioned embodiment. The liquidus temperature TL=1513° C. and the solidus temperature TS=1472° C. calculated from the Hirai equation.
Below, the common conditions of the manufacturing method of a thin cast piece are shown.

Cooling roll diameter: 1200mm
Casting width: 800mm
Casting thickness: 2.0 mm on average
Casting speed: 50m/min on average
Casting atmosphere: Ar+N ₂
Casting amount: 10 tons, molten metal level arc angle: 40 deg
Contact arc length of molten steel and cooling roll drum: 419 mm
Outside dimension width of pouring nozzle: 400 mm
Pouring nozzle discharge port: Width 350 mm, height 15 mm, single slit on one side. When immersed, the top of the discharge port is 10 mm deep.
Target molten steel temperature of molten steel pool part: 1543°C (Since the liquidus temperature TL of the above molten steel is 1513°C, the target superheat is 30°C)

Then, the scum weir of the material shown in Table 1 was used. In this embodiment, the test No. 21 and No. 21. Except for No. 22, the entire scum weir was made of a conductive refractory (AG: alumina graphite. C content: 20 mass%) to be an electric heating section. The current-carrying electrodes were arranged by screwing graphite electrodes whose ends were screwed to both sides in the width direction of the molten steel dipping portion of the AG scum weir. Test No. 22 was made of non-conductive BN.

The scum weir had a thickness of 10 mm. Table 1 shows the width of the scum weir, the position in the width direction where the scum weir is arranged, and the immersion depth (at a molten metal level of 40 deg). The widthwise position where the scum weir is arranged is indicated by the distance from one end of the thin cast piece in the range where the scum weir exists (Table 1). Therefore, the center position of the scum weir in the width direction is the test number. Except for 25 and 26, the widthwise center position of the thin cast piece is 400 mm. The pouring nozzle discharge port has a width of 350 mm, and the nozzle is arranged at the center of the width. When the width direction position of the nozzle discharge port is represented by the distance from one end of the thin cast piece as in the scum weir, the position is 225 to 575 mm. Therefore, if there is a scum weir over at least this range, the scum weir will face the entire discharge port. Test No. No. 1 is an example in which the scum weir having the same width as the discharge port faces the entire discharge port. Then, the test No. 2 to 11 are examples in which scum weirs having a discharge port width of 350 mm or more are opposed to each other over the entire discharge port. The surface temperature of the molten steel immersion portion was measured by a radiation thermometer at the time of electric heating immediately before the start of casting and is shown in Table 1.

Casting of thin-walled slabs was carried out under the conditions as described above, and the state of metal adhesion to the scum weir, the number of hot bands generated, the scum entrainment area ratio, and the number of surface cracks were evaluated as follows.

(Scum weir metal attachment status)
After the completion of casting, the surface of the scum weir was visually observed to confirm the adhesion of metal. "A" when no metal was confirmed, "B" when the metal adhesion was confirmed only in the molten steel immersion area near the molten steel surface equivalent position, or when the area ratio of the immersion area was less than 20%, molten steel immersion When the area ratio of the area is 20% or more, the adhesion of the metal is confirmed, and when the maximum thickness of the metal is less than 1 mm, it is "C". In addition, the case where the maximum thickness of the metal was 1 mm or more was evaluated as "D". The evaluation results are shown in Table 1.

(Number of hot bands generated)
The number of hot bands generated within 1 minute from the start of casting was measured from the recorded video. The evaluation results are shown in Table 1.

(Scum area ratio)
The surface of the thin cast piece having a length of 1 m and having a full width of 1 m was visually observed to mark the scum winding portion, and the area ratio was measured by image processing. The evaluation results are shown in Table 1.

(Number of surface cracks)
The thin-walled slab in the stationary part was visually observed and 8 times magnified on the surface of the entire width of 1 m in length to evaluate the number of cracks having a length of 2 mm or more per 1 m ² . The evaluation results are shown in Table 1.

Test No. In No. 21, since the scum weir was not used, a large amount of scum was involved and there were many slab cracks. The test No. The hot band generated in No. 21 is generated when the metal generated on the surface of the side weir is caught and is not related to the scum weir.
Test No. In No. 22, a scum weir made of BN, which is a non-conductive refractory, is used and does not have an electric heating section. For this reason, preheating cannot be performed by electric heating, and a large amount of metal adheres to the molten steel dipping portion, and the metal peels off and is involved, resulting in frequent occurrence of hot bands. Since the conditions (width, position, immersion depth) as the scum weir were sufficient, the scum winding area ratio was 10% or less as a result of being able to sufficiently suppress the scum winding on the peripheral surface of the cooling roll. The surface of the thin cast piece was not cracked.

Test No. In No. 23, since electric heating was not carried out, a large amount of metal was attached to the molten steel dipping portion, and the metal was peeled off and caught, so that hot bands frequently occurred. Since the conditions (width, position, immersion depth) as a scum weir were sufficient, the scum entrainment on the peripheral surface of the cooling roll could be sufficiently suppressed, and as a result, the scum enrollment area ratio was 10% or less, and thin casting There was no surface crack on the piece.

Test No. In No. 24, the molten steel immersion portion was heated by electric heating, so that the adhesion of the metal was suppressed. However, since the width of the scum weir was narrower than that of the nozzle discharge port, the scum was directly transferred from the part exceeding the scum weir width to the chill roll side and caught therein.
Test No. In No. 25, the molten steel immersion portion was heated by electric heating, so that the adhesion of the metal was suppressed. However, although the scum weir width was 550 mm, which was larger than the nozzle discharge port width, the position in the width direction was not appropriate and did not face the entire width of the nozzle discharge port. Therefore, the scum was directly wound around the cooling roll from the portions not facing each other.
Test No. In No. 26, the molten steel immersion part was heated by electric heating, so that the adhesion of the metal was suppressed. However, the scum weir is not arranged in the center of the width, two scum weirs with a width of 100 mm, near the triple point near the edge portions on both sides (20 to 20 at the width direction position indicated by the distance from one end of the thin cast piece). Since it was arranged at 120 mm and 680 to 780 mm), a large amount of scum was rolled in from the central portion of the width of the cooling roll, and cracking occurred.

On the other hand, the test No. In Nos. 1 to 11, since the molten steel immersed portion was heated by electric heating, Test No. 1 in which the molten steel immersed portion was not heated. As compared with No. 23, as a result of less amount of metal adhered to the scum weir dipping portion, hot bands due to metal separation and entrapment were less. Since the scum weir satisfied the sufficient conditions (width, position, immersion depth), scum entrainment was small and slab cracking was suppressed.

In particular, the test No. in which the preheating was performed so that the surface temperature Tsf of the molten steel immersed portion satisfied the above-mentioned formula (1). In Nos. 1 to 10, adhesion of metal was suppressed, and generation of hot bands could be further suppressed.
Further, the test No. in which the preheating was carried out so that the surface temperature Tsf of the molten steel immersed portion satisfied the above-mentioned formula (21). In No. 9, the adhesion of metal was further suppressed, and the generation of hot bands was eliminated.

From the above results, it was confirmed that, according to the present invention, the generation of metal on the surface of the scum weir can be suppressed at least at the start of casting, and stable casting can be performed.

1 Thin cast slab 3 Molten steel 5 Solidified shell 11 Cooling roll 16 Molten steel pool part (molten metal pool part)
20 Scum Weir 20a Molten Steel Immersion Part (Molten Metal Immersion Part)
21 Weir body 22 Electric heating unit

Claims (6)

A molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams is supplied with molten metal through a pouring nozzle to form and grow a solidified shell on the peripheral surface of the cooling roll to form a thin wall casting. In a twin roll type continuous casting apparatus for manufacturing a piece, a scum weir disposed in the molten metal pool section so as to face the discharge port of the pouring nozzle,
A scum weir, comprising: an electric heating part for heating a molten metal immersion part immersed in the molten metal in the molten metal pool part. The scum weir according to claim 1, wherein the electric heating unit is made of a conductive refractory material. The scum weir according to claim 1 or 2, wherein an insulating refractory layer is formed on at least the surface of the molten metal immersion portion. A molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams is supplied with molten metal through a pouring nozzle to form and grow a solidified shell on the peripheral surface of the cooling roll to form a thin wall casting. A twin roll type continuous casting apparatus for manufacturing a piece,
The twin roll, wherein the scum weir according to any one of claims 1 to 3 is arranged in the molten metal pool portion so as to face a discharge port of the pouring nozzle. Type continuous casting equipment. A molten metal pool portion formed by a pair of rotating cooling rolls and a pair of side dams is supplied with molten metal through a pouring nozzle to form and grow a solidified shell on the peripheral surface of the cooling roll to form a thin wall casting. A method of manufacturing a thin cast piece for manufacturing a piece,
The scum weir according to any one of claims 1 to 3 is arranged in the molten metal pool portion so as to face a discharge port of the pouring nozzle,
At least before the start of casting, the molten metal immersion part is heated by the electric heating part, and a method for producing a thin cast piece is characterized. The molten metal is molten steel, and the surface temperature Tsf of the molten metal immersion part is heated by the electric heating part so as to satisfy the following expression (1). Method for manufacturing thin cast slab.
Formula (1): Tsf≧TL−0.7×(TL−TS)−0.92×(ΔTm+0.7×(304+TL−TS))
TL: liquidus temperature, TS: solidus temperature, ΔTm: superheat in molten metal pool part

Images