JP2001096339A - Apparatus for producing thin cast piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin casting piece casting device capable of restricting and controlling heat stream from molten metal to a cooled body by reducing the contact area of the surface of the transferring cooled body such as a cooling drum with the molten metal. SOLUTION: In a thin casting piece casting device which supplies molten metal to the surface of the transferring cooled body such as a cooling drum and supplies a mixed gas of the absorptive gas with a non-absorptive gas between the surface of the cooled body and the molten metal to cast a thin casting piece with supplying a molten metal on the surface of the cooling body that a thinning such as a cooling drum is moved and which molds light metal mold piece. By forming hollows so as to overlap each other on the surface of the cooled body, they adjoin each other through ridges. It is composed that the surface of the cooled body and a molten metal may be brought into the line contact or a point contact in a plurality of projections gathered together.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for casting a thin cast slab which supplies molten metal to the surface of a moving cooling body and solidifies it, and is useful when applied to a twin drum type continuous casting apparatus and the like. .

[0002]

2. Description of the Related Art Continuous casting apparatuses for thin cast slabs include a twin-drum type, a single-drum type, and a drum-belt type, which include a moving cooling body such as a drum or a belt as a part of a mold. It is.

FIG. 6 shows a configuration example of a conventional twin-drum type continuous casting apparatus. As shown in the figure, the twin-drum continuous casting apparatus has a pair of cooling drums 3 rotating in opposite directions as indicated by arrows in the figure as moving cooling bodies. Above the cooling drum 3, a tundish 1 for containing a molten metal (melt) 8 is provided. A pouring nozzle 2 is connected to a lower end of the tundish 1, and a tip (lower end) of the pouring nozzle 2 extends to a lower pool 7. The pool 7 is formed by a pair of cooling drums 3 and a pair of short side weirs (side weirs) 6 provided on both axial sides of the cooling drum 3.

[0004] A seal chamber 5 is provided between the tundish 1 and the cooling drum 3 for shutting off the pool 7 from the atmosphere. A seal gas supply pipe 4 is connected to the seal chamber 5, and a seal gas such as nitrogen gas is continuously supplied into the seal chamber 5 through the seal gas supply pipe 4. Incidentally, reference numeral 10 in FIG. 6 denotes a cleaning brush for cleaning the surface of the cooling drum 3.

In this twin-drum type continuous casting apparatus, the molten metal 8 of the tundish 1 is accumulated in the pool 7 through the pouring nozzle 2, cooled by the rotating cooling drum 3 and solidified, thereby forming a thin-walled casting. Strips 9 are cast continuously. At this time, since the seal gas is supplied to the seal chamber 6 via the seal gas supply pipe 4, the thin cast piece 9 is cast in the seal gas atmosphere.

In the continuous casting apparatus, a concave portion (dent) 3-1 as shown in FIG. 7 is formed on the surface of the cooling drum 3 for the purpose of smoothing the surface of the thin cast slab 9 and the like.
Are disclosed in Japanese Patent Publication No. 5-23860 and Japanese Patent Publication No. 5-81346.

That is, the cooling drum 3 which is a moving cooling body
In the continuous casting direction of a thin cast piece in which the molten metal 8 is supplied to the surface of the cooling drum 3 and solidified to continuously cast the thin cast piece 9, Japanese Patent Publication No. 23860/1993 discloses that “the surface of the cooling drum 3 has a diameter of 0 mm. A concave portion 3-1 having a depth of 2 μm to 100 μm having a circular or oval opening of 1 mm to 1.2 mm is provided without contact with each other, and the molten metal supplied to the surface of the cooling drum 3 during continuous casting operation. 8 is filled with a mixed gas of a nitrogen gas and an inert gas, which is easily absorbed by the metal, to suppress excessive retention of the gas between the molten metal 8 and the concave portion 3-1 so as to suppress each of the concave portions 3-1. Method of Continuous Casting of Thin-Walled Slabs, characterized by Breaking the Gas Gap "
Is provided.

In Japanese Patent Publication No. 5-81346,
"Molten metal-absorbing (soluble) gas and non-absorbing (non-soluble) gas are supplied to a pool 7 formed between a pair of cooling drums 3 each having a cooling mechanism inside and having a concave portion 3-1 on the surface. And continuously casting the thin cast piece 9 in the mixed gas atmosphere.

[0009]

However, in the former (Japanese Patent Publication No. 5-23860) continuous casting method,
The shape of the opening of the recess 3-1 formed on the surface of the cooling drum 3 is limited to a circle or an oval.
Are provided without contacting each other, so that the recess 3-1 is provided.
The gas gap is divided by making a surface contact between the portion between the metal portion and the other concave portion 3-1 and the molten metal 8 so that no gas exists in the contact portion.

That is, in the former continuous casting method, since the cooling drum 3 and the molten metal 8 are in surface contact with each other, the contact area between them is large, and the amount of heat transferred from the molten metal 8 to the cooling drum 3 via this contact surface. Is very large, it is difficult to limit and control the flow of heat from the molten metal 8 to the cooling drum 3. For this reason, the surface of the cooling drum 3 and its vicinity may become extremely hot. In this case, since the change range of the temperature cycle repeatedly generated on and near the surface of the cooling drum 3 becomes large, cracks are easily generated on the surface of the cooling drum 3 and its vicinity. If cracks occur in the cooling drum 3, it becomes impossible to continue casting of the thin cast piece 9.

Also, in the latter continuous casting method (Japanese Patent Publication No. 5-81346), the recess 3-1 is provided without contacting each other, and the recess 3-1 and the other recess 3 are provided.
-1 and the molten metal 8 come into surface contact with each other, and therefore have the same problem as described above.

In view of the above problems, the present invention reduces the contact area between the surface of a moving cooling body such as a cooling drum and the molten metal to restrict the flow of heat from the molten metal to the cooling body, and It is an object to provide a thin cast slab casting apparatus that can be controlled.

[0013]

Means for Solving the Problems A first method for solving the above problems is described below.
The thin cast slab casting apparatus of the present invention supplies a molten metal to a surface of a moving cooling body and supplies a mixed gas of an absorbing gas and a non-absorbing gas between the surface of the cooling body and the molten metal. In a thin-walled slab casting apparatus for casting slabs, by forming concave portions on the surface of the cooling body so as to overlap, adjacent concave portions contact each other across a ridge line, and cooling is performed at a convex portion where a plurality of ridge lines are gathered. It is characterized in that the surface of the body and the molten metal are in line contact or point contact.

Further, a thin cast slab casting apparatus according to a second invention is characterized in that, in the thin cast slab casting apparatus according to the first invention, the unevenness depth of the surface of the cooling body is in a range of 40 μm to 200 μm. .

The thin cast slab casting apparatus of the third invention is the thin cast slab casting apparatus of the first or second invention, wherein the volume ratio of the non-absorbable gas in the mixed gas is 1% to 55% at room temperature. It is characterized by the following.

The thin cast slab casting apparatus of the fourth invention is the thin cast slab casting apparatus of the first, second or third invention, wherein the size of one recess is such that the diameter of the area surrounded by the ridgeline is 2m
m or less.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an external view of a surface of a cooling drum in a continuous casting apparatus for a thin cast piece according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a part of the surface of the cooling drum shown in FIG. FIG. FIG. 3 is an explanatory view showing the operation when only the absorbing gas is used as the sealing gas in the continuous casting apparatus. FIG. 4 is a diagram showing the sealing of the mixed gas of the absorbing gas and the non-absorbing gas in the continuous casting apparatus. FIG. 5 is an explanatory view showing an operation when the gas is used as a gas, and FIG. 5 is a graph showing a relationship between a concave-convex depth and a heat flux reduction rate.

The overall structure of the continuous casting apparatus is the same as the conventional one, and the description and illustration thereof are omitted here (see FIG. 6).

<Construction> As shown in FIGS. 1 and 2, in the continuous casting apparatus of the present embodiment, the recess 14 is formed so as to overlap the surface of the cooling drum 3 which is a moving cooling body. Adjacent recesses 14 are in contact with each other with a ridge 11 interposed therebetween, and the surface of the cooling drum 3 and the molten metal 8 are configured to make line contact or point contact with each other at a convex portion 15 in which a plurality of the ridges 11 are gathered.

That is, FIG. 1 shows the appearance of a part of the surface of the cooling body 3, and the line in the figure represents the ridge 11 of the unevenness. The portion surrounded by the ridge line 11 is the concave portion 14.
And three (sometimes more than three) ridge lines 1
The portion where 1 is gathered is the convex portion 15. Therefore, the surface of the cooling body 3 and the molten metal 8 are geometrically regulated so as to make a line contact or a point contact at the convex portion 15 (see FIGS. 3 and 4, detailed later). Also, the recess 14
It is acceptable that the sealing gas existing in the other recess 14 is connected to the sealing gas existing in the other concave portion 14.

The irregular shape as described above has a diameter of, for example, 1 m.
It is formed by a method of colliding a granular object such as a steel ball having a diameter of m to 5 mm with the surface of the cooling body 3 or a method of pressing an object having a spherical or irregularly shaped convex portion on the surface of the cooling body 3. be able to. Also, the unevenness may be formed by a method of applying a streak-like, lattice-like or spherical processing by machining, a method of electric discharge machining, or the like.

The shape of the opening of the concave portion 14 is not limited to a specific shape (circular, oval, etc.), but may have various shapes as shown in FIG. Further, the uneven shape may be irregular as shown in FIG. According to the method of causing the granular object to collide with the surface of the cooling body 3, such irregularly shaped irregularities are formed.

<Operation / Effect> According to the continuous casting apparatus having the above configuration, the following operation / effect can be obtained (FIGS. 1 to 6).
reference).

During the continuous casting of the thin cast slab 9, the molten metal 8
Moves forward as if wetting the irregularities formed on the surface of the cooling drum 3 while removing the sealing gas on the surface of the cooling drum 3. For this reason, although the sealing gas is removed from the convex portion 15 on the surface of the cooling drum and the molten metal 8 comes into contact with the molten metal 8, the concave portion 14 is provided on the surface of the cooling drum 3 and the effect of the surface tension of the molten metal 8 causes In the concave portion 14 on the surface, the sealing gas remains as a thin layer (gas gap layer).

However, at this time, when only the absorbing gas such as nitrogen gas is supplied as the sealing gas into the sealing chamber 5 to cast the thin cast piece 9, the surface of the cooling drum 3 in this case is shown in FIG. As shown in the figure, the gas gap layer 22 between the recess 14 on the surface of the cooling drum and the molten metal 8 becomes extremely thin.
In FIG. 3, reference numeral 25 denotes a contact portion of the molten metal 8 with the convex portion 15 on the cooling drum surface, reference numeral 21 denotes a contact portion of the molten metal 8 with the ridge line 11 on the cooling drum surface, and reference numeral 20 denotes a cooling drum surface of the molten metal 8. Is a non-contact portion with the concave portion 14.

That is, since the absorbing gas such as nitrogen gas which is easily absorbed by the metal is quickly absorbed into the molten metal 8, the pressure of the sealing gas decreases, and accordingly, the molten metal 8
Of the cooling drum 3 and the shape of the recesses 14 on the surface of the cooling drum 3
The gas gap layer 22 becomes very thin. For this reason, heat transfer from the high-temperature molten metal 8 to the cooling drum 3 is performed quickly, and the surface temperature of the cooling drum 3 is significantly increased. Its size depends on the material, structure and casting parameters of the cooling drum 3, but for example, 4
It may reach 20 ° C to 600 ° C or more.

On the other hand, when a thin mixed slab 9 is cast by supplying a mixed gas containing an inert gas (non-absorbing gas) in an absorbing gas as a sealing gas to the sealing chamber 5, FIG. 4 shows a positional relationship between the surface of the cooling drum 3 and the molten metal 8 in this case, and a gas gap layer 22 having a sufficient thickness is held between the concave portion 14 on the surface of the cooling drum and the molten metal 8. Is done. In addition, 25 in FIG. 4 is a contact portion of the molten metal 8 with the convex portion 15 on the surface of the cooling drum.
Is a non-contact portion of the molten metal 8 with the surface of the cooling drum.

That is, a non-absorbable gas such as an argon gas sandwiched between the concave portion 14 on the surface of the cooling drum and the molten metal 8 is not absorbed or hardly absorbed by the molten metal 8 and thus remains in place. For this reason, an appropriate space can be generated between the surface (the concave portion 14) of the cooling drum 3 and the molten metal 8. As a result, the amount of heat transfer from the molten metal 8 to the cooling drum 3 is reduced, so that the surface temperature of the cooling drum 3 can be kept low, for example, 300 ° C. to 450 ° C.

That is, in the continuous casting apparatus of the present embodiment, the concave portions 14 are formed on the surface of the cooling drum 3 so as to overlap with each other, so that the adjacent concave portions 14
1 are in contact with each other.
In the above, since the surface of the cooling drum 3 and the molten metal 8 are configured to make a line contact or a point contact, the contact area between the surface of the cooling drum 3 and the molten metal 8 is greatly reduced as compared with the related art. By supplying a mixed gas containing an appropriate amount of the absorptive gas between the surface of the cooling drum 3 and the molten metal 8, the surface of the cooling drum 3 (the concave portion 14) and the molten metal 8
Since a suitable distance can be generated between the molten metal 8 and the cooling drum 3, the amount of heat transfer from the molten metal 8 to the cooling drum 3 can be reduced, and the surface temperature of the cooling drum 3 can be kept low. Casting can be performed.

That is, since the amount of heat transfer from the molten metal 8 to the cooling drum 3 can be specified by appropriately adjusting the content (volume ratio) of the non-absorbable gas, the casting per unit time can be performed. While maintaining a relatively high weight, the heat load on the cooling drum 3 can be reduced to reduce the temperature rise on the surface of the cooling drum 3 and the vicinity thereof. And
As described above, since the temperature rise on the surface of the cooling drum 3 and its vicinity can be reduced, the change range of the temperature cycle repeatedly generated near the surface of the cooling drum 3 can be reduced. Cracks on the surface and its vicinity can be prevented, or the total casting amount up to the cracks can be increased.

In this case, the surface of the cooling drum 3 (the concave portion 14) is adjusted by adjusting the content of the non-absorbable gas.
The amount of heat transfer from the molten metal 8 to the cooling drum 3 can be changed by changing the distance between the molten metal 8 and the molten metal 8, so that the heat load acting on the cooling drum 3 during casting can be arbitrarily adjusted. it can. The adjustment of the amount of heat transfer from the molten metal 8 to the cooling drum 3 by adjusting the content of the non-absorbable gas can be performed even during casting.

Further, the larger the unevenness depth of the cooling drum 3 (the difference between the height of the projections and the height of the recesses), regardless of the content of the non-absorbable gas (increased even if the content is reduced). It was also found that good castability could be maintained.

From the results of the test shown in FIG. 5, the depth of the irregularities on the surface of the cooling body 3 is suitably in the range of 40 μm to 200 μm. That is, as shown in FIG.
Cracks occurred in the thin cast slab 9 in the region of μm or less, and excessive segregation occurred in the region of the unevenness depth of 200 μm or more.

As a result of the test, the volume ratio of the non-absorbable gas in the mixed gas (seal gas) was 1% to 55% at room temperature.
The range of% was appropriate.

Further, as a result of the test, the size of one recess 14 was good for the castability of the thin cast piece 9 when the diameter of the area surrounded by the ridgeline 11 was 2 mm or less.

[Embodiment] Here, a specific embodiment will be described.

A pair of water-cooled drums (cooling drums) for cooling the molten metal in contact with the surface through cooling water is used therein, and a twin-drum type thin cast continuous casting apparatus in which the water-cooled drums rotate in opposite directions is used. Was. Irregularities as illustrated in FIGS. 1 and 2 were formed on the surface of the water-cooled drum by colliding steel balls having a diameter of 2.5 mm. 18Cr-8Ni austenitic stainless steel was used as the molten metal. Casting speed is 30m / min to 80m / min on average
And During casting, the surface of the water-cooled drum was cleaned with a cleaning brush.

The results of this example are shown in Table 1. As shown in the table, when the volume ratio of the argon gas in the mixed gas (seal gas) of the nitrogen gas as the absorbing gas and the argon gas as the non-absorbing gas is 1% to 55% (No. Also in No. 8), the average heat flux transmitted from the molten metal 8 to the cooling drum 3 is reduced as compared with the case where the volume ratio of the argon gas is 0% (No. 9 and No. 10).

[0040]

[Table 1]

As in this embodiment, the contact area between the surface of the water-cooled drum and the molten metal is reduced by colliding steel balls against the surface of the water-cooled drum to form irregularities as illustrated in FIGS. Very small (line or point contact)
In addition, inert gas (non-absorbable gas) in the seal gas
By keeping the distance between the surface (recess) of the water-cooled drum and the molten metal by mixing the water, the amount of heat transfer from the molten metal to the water-cooled drum is reduced, and the heat load applied to the water-cooled drum is reduced.

Further, when the depth of the concavities and convexities increases, the amount of heat transfer from the molten metal to the water-cooled drum can be greatly reduced even with a small amount of non-absorbable gas.

As a result, the change range of the temperature cycle repeatedly generated near the surface of the water-cooled drum is reduced, so that the occurrence of thermal fatigue cracks or the like can be prevented or the occurrence of thermal fatigue cracks or the like can be significantly reduced. Became.

[0044]

As described above in detail with the embodiments of the present invention, the thin cast slab casting apparatus of the first invention supplies molten metal to the surface of the moving cooling body, In a thin-walled slab casting apparatus for casting a thin-walled slab by supplying a mixed gas of an absorbing gas and a non-absorbing gas between the molten metal, by forming a concave portion so as to overlap the surface of the cooling body. Adjacent recesses are in contact with each other across a ridge line, and the surface of the cooling body and the molten metal are in line contact or point contact with each other at a convex portion in which a plurality of the ridge lines are gathered.

Therefore, according to the thin cast slab casting apparatus of the first invention, the concave portions are formed on the surface of the cooling body so as to overlap with each other, so that adjacent concave portions contact each other with the ridge line interposed therebetween. Since the surface of the cooling body and the molten metal are configured to be in line contact or point contact with each other at the gathered convex portions, the contact area between the surface of the cooling body and the molten metal is significantly reduced as compared with the related art. By supplying a mixed gas containing an appropriate amount of the absorptive gas between the surface of the cooling body and the molten metal, an appropriate gap can be generated between the surface (recess) of the cooling body and the molten metal. In addition, the amount of heat transfer from the molten metal to the cooling body can be reduced, and the surface temperature of the cooling body can be kept low, and good casting can be performed.

That is, since the amount of heat transfer from the molten metal to the cooling body can be specified by appropriately adjusting the content (volume ratio) of the non-absorbable gas, the casting weight per unit time can be reduced. While maintaining a relatively high level, the heat load on the cooling body can be reduced to reduce the temperature rise on the surface of the cooling body and its vicinity. Since the temperature rise on the surface of the cooling body and the vicinity thereof can be reduced in this way, the range of change in the temperature cycle that repeatedly occurs near the surface of the cooling body can be reduced, so that the cooling body Preventing cracks on the surface and its vicinity,
Alternatively, the total casting amount up to the occurrence of cracks can be increased.

The shape of the opening of the recess is not limited to a specific shape (circular, oval, etc.), but may have various shapes. Further, the irregular shape may be irregular. In addition, it is acceptable that the seal gas existing in the concave and convex portions and the seal gas existing in other concave portions are connected.

The thin cast slab casting apparatus of the second invention is characterized in that, in the thin cast slab casting apparatus of the first invention, the unevenness depth of the surface of the cooling body is in the range of 40 μm to 200 μm. .

The thin cast slab casting apparatus of the third invention is the thin cast slab casting apparatus of the first or second invention, wherein the volume ratio of the non-absorbable gas in the mixed gas is 1% to 55% at room temperature. It is characterized by the following.

The thin cast slab casting apparatus according to the fourth aspect of the present invention is the thin cast slab casting apparatus according to the first, second or third aspect, wherein the size of one recess is such that the diameter of the area surrounded by the ridge line is smaller. 2m
m or less.

Therefore, according to the thin cast slab casting apparatus of the second, third or fourth aspect of the present invention, the unevenness depth of the cooling body surface is reduced to 40
by setting the volume ratio of the non-absorbable gas to 1% to 55%, or by setting the size of one concave portion to be 2 mm or less in the range surrounded by the ridge line, thereby improving the castability. Better.

[Brief description of the drawings]

FIG. 1 is an external view of a surface of a cooling drum in a continuous casting apparatus for a thin cast slab according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of the surface of the cooling drum shown in FIG.

FIG. 3 is an explanatory view showing an operation when only an absorbent gas is used in the continuous casting apparatus.

FIG. 4 is an explanatory diagram showing an operation when a mixed gas of an absorbing gas and a non-absorbing gas is used in the continuous casting apparatus.

FIG. 5 is a graph showing a relationship between a concave-convex depth and a heat flux reduction rate.

FIG. 6 is a configuration diagram of a conventional twin drum type continuous casting apparatus.

FIG. 7 is a cross-sectional view showing a concavo-convex shape on the surface of a conventional cooling drum.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tundish 2 Pouring nozzle 3 Cooling drum 4 Seal gas supply pipe 5 Seal chamber 6 Short side weir (side weir) 7 Hot water pool part 8 Molten metal 9 Thin cast piece 10 Cleaning brush 11 Edge line 14 Concave part 15 Convex part

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Keiichi Yamamoto, Inventor 4-6-1-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Inside the Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Kunimasa Sasaki 4-chome, Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. 6-22 Mitsubishi Heavy Industries, Ltd.Hiroshima Works (72) Inventor Ritsuo Hashimoto 6-22, Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Research Center (72) Inventor Kanji Hayashi Hiroshima Nishi-ku, Hiroshima City 4-62 Kannon Shinmachi Mitsubishi Heavy Industries, Ltd. Hiroshima Works F-term (reference) 4E004 AA07 DA11 DA12 DA13 DA22 MC01 QA01 QB01

Claims (4)

[Claims] 1. A molten metal is supplied to a surface of a moving cooling body, and a mixed gas of an absorbing gas and a non-absorbing gas is supplied between the surface of the cooling body and the molten metal to cast a thin cast slab. In the thin cast slab casting device, by forming the concave portion on the surface of the cooling body so as to overlap, adjacent concave portions contact each other across a ridge line, and in the convex portion where a plurality of ridge lines are gathered, the convex portion formed by the ridge line is in contact with the surface of the cooling body. A thin cast slab casting apparatus characterized in that the molten metal is in line contact or point contact. 2. The thin cast slab casting apparatus according to claim 1, wherein the unevenness depth of the surface of the cooling body is in a range of 40 μm to 200 μm. 3. The thin cast slab casting apparatus according to claim 1, wherein the volume ratio of the non-absorbable gas in the mixed gas is from 1% at room temperature.
A thin-walled slab casting apparatus characterized in that the thickness is 55%. 4. The thin cast slab casting apparatus according to claim 1, wherein the size of one recess is 2 mm in diameter in a range surrounded by a ridge.
mm or less.