JP2003039139A - Scum bank of twin drum type continuous casting machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scum bank of a twin drum type continuous casting machine having a heat-resistant and shock-resistant property, and no bad influence on quality of a slab, and manufacturing at low cost. SOLUTION: In a twin drum type continuous casting machine casting a thin metal sheet belt 5 by supplying molten steel 4 in a pouring basin portion 3 formed by a pair of cooling drums 1 and a pair of side banks 2, a pair of scum banks 6 arranged along a widthwise direction of the cooling drum of the pouring basin portion 3 are provided with 3 to 15 mass % of graphite and 60 to 90 mass % of a metallic oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-drum continuous casting machine for producing a metal strip, and more particularly to a scum weir arranged in a pool of molten metal.

[0002]

2. Description of the Related Art A twin-drum continuous casting machine will be described with reference to FIG. The twin-drum continuous casting machine is a basin formed by a pair of cooling drums 1 and 1 rotating in the direction of an arrow and a pair of side dams 2 (shown by phantom lines) pressed against both end faces of the pair of cooling drums. Part 3 and nozzle 5 for supplying molten steel 4 to the pool 3
And a pair of scum weirs 6, 6 arranged by immersing a part thereof in the molten steel 4 between the nozzle 5 and the cooling drum 1. The flow of the molten steel discharged from the nozzle 5 causes the meniscus portion R to be ruffled and deteriorates the surface property of the metal ribbon S. Therefore, the scum weir 6 relaxes the molten steel flow to prevent the meniscus portion R from being ruffled. There is (JP-A-61-1652)
(See Japanese Patent No. 55). Such a scum weir is thin and
Since high-temperature molten steel comes into direct contact with the steel, heat resistance and thermal shock resistance are required. Therefore, a boron nitride (BN) material is generally used.

[0003]

However, when a scum weir made of BN material is used for a long time, the portion immersed in the molten steel reacts with the molten steel and dissociates, and the dissociated B or N dissolves in the molten steel. As a result, the components on the surface of the slab are locally changed, causing a gloss defect on the surface of the slab. Further, the dissociated B reacts with oxygen in the molten steel to form boron oxide (B2O3), which causes surface cracking of the slab.

On the other hand, there has been proposed a method of forming a protective film such as Al ₂ O ₃ or ZrO _{2 on} the surface of BN by means of thermal spraying or coating in order to make up for the drawbacks of BN described above (JP-A-4-253552). (See the official gazette). However, even when this scum weir is used for a long time, the protective film is easily peeled off due to the difference in thermal expansion with BN and the influence of molten steel flow, and the peeled protective film causes a slab surface defect. It is difficult to exert it stably over time. Further, since the base material BN is expensive and the processing cost of the protective film is high, it is difficult to put it into practical use in terms of cost.

The present invention solves the above-mentioned problems, and by using a graphite-metal oxide system as the refractory for the scum weir, the scum weir material has high thermal shock resistance and high corrosion resistance, Another object of the present invention is to provide a scum weir for a twin-drum continuous casting machine that simultaneously satisfies the characteristics that the quality of the cast slab is not adversely affected and that the cost is low.

[0006]

A scum weir of a twin-drum continuous casting machine according to the present invention which solves the above-mentioned problems, supplies molten steel to a molten metal pool formed by a pair of cooling drums and a pair of side weirs. In an apparatus for casting a metal ribbon, a pair of scum weirs arranged along the width direction of the cooling drum of the molten metal pool, wherein the scum weirs are 3 to 15 mass% graphite and 6
It is a scum weir composed mainly of 0 to 90 mass% metal oxide.

The graphite has a maximum particle size of 300 μm.
Hereinafter, it is preferable that the average particle size is 100 μm or less, the maximum particle size of the metal oxide is 100 μm or less, and the average particle size is 50 μm or less, and the main components of the metal oxide are ZrO ₂ and Al ₂ It is preferably one or two of O ₃ .

In addition, the scum weir of another twin-drum continuous casting machine of the present invention which solves the above-mentioned problems, a molten metal is supplied to a molten metal pool portion formed by a pair of cooling drums and a pair of side weirs. A pair of scum weirs arranged along the width direction of the cooling drum of the molten metal pool, wherein the scum weir has a bending strength of 12 MPa or more and a thermal expansion coefficient of 7 × 10 ^−6. (1 / ° C) or less, thermal conductivity of 3 to 15 W / m
It is characterized by being K.

Based on the experience of long-time casting and the above-mentioned knowledge, the present inventors arranged the characteristics that the scum weir should have as follows. 1) 15 with or without preheating
It has a thermal shock resistance that does not cause cracking even when immersed in molten steel above 00 ° C. 2) A slab that does not lose its scum weir function due to melting loss even during long-term casting of about 5 hours, and is also caused by contamination of molten steel. Corrosion resistance without defects 3)
Even if the refractory particles fall off due to molten steel flow, etc., the particle size must be such that this does not form the surface of the slab. 4) Even if it is thin, it does not crack due to the force received during molten steel flow or peeling of the adherent metal. 5) Since it is usually used by fixing it to an iron plate, it has volume stability (low thermal deformation) to the extent that it does not crack due to expansion or warpage of refractory materials. 6)
The six points are that it is a practical cost.

Among the above characteristics, the present invention is 1), 5),
From the viewpoint of satisfying 6), 3 to 15 mass% of graphite is contained, and the metal oxide is selected from the viewpoint of 2), and the maximum particle size is 300 μm or less and the average particle size is 100 μm.
The maximum particle size is 1 after containing 3 to 15 wt% of graphite of m or less.
The characteristics of 3) and 4) can be further satisfied by blending a metal oxide having a particle diameter of 00 μm or less and an average particle diameter of 50 μm or less as the remaining main component. 1), 4),
Among the numerical values that serve as indicators for 5), 1) is thermal conductivity: 3 to
15 W / mK, 4) Bending strength: 12 MPa or more, 5)
Can be defined by a thermal expansion coefficient: 7 × 10 ⁻⁶ (1 / ° C.) or less, and one or two kinds of ZrO ₂ and Al ₂ O ₃ are optimal as the metal oxide.

That is, if the content of graphite is less than 3%, cracking occurs during use due to insufficient thermal shock resistance and excessive thermal deformation. Further, if the graphite content exceeds 15%, not only the strength is significantly reduced, but also the oxidative decarburization reaction due to the atmosphere and molten steel progresses rapidly, and the amount of melting loss increases. If the metal oxide content is less than 60%, the melting loss becomes severe when used for a long time, resulting in 90%.
If it is over, cracks will occur in the scum weir due to poor thermal shock resistance. Further, the maximum particle size of graphite is more than 300 μm, the average particle size is more than 100 μm, the maximum particle size of metal oxide is more than 100 μm,
When the average particle diameter is more than 50 μm, when the refractory particles fall off due to molten steel flow or the like, defects are likely to occur on the surface of the cast piece. Moreover, if the bending resistance of the scum weir refractory is 12 MPa or more, the coefficient of thermal expansion is 7 × 10 ⁻⁶ (1 / ° C.) or less, and the thermal conductivity is out of the range of 3 W / mK or more, thermal shock resistance and strength are insufficient. Also, due to excessive thermal deformation, cracking occurs during use, and if the thermal conductivity exceeds 15 W / mK, the adhesion of metal to the scum weir becomes noticeable, which hinders operation.

In addition to graphite and metal oxides, the following commonly used compounds may be added in a total amount of 25% or less. For example, S as an antioxidant
It is also possible to add non-oxides such as iC and B ₄ C, or to add metals such as Si and Al to improve strength and prevent oxidation. Further, as carbonaceous raw materials other than graphite, pitch, Carbon black or the like can be added to improve the strength and densify the structure. As the metal oxide, Z
When rO ₂ is used, it is generally CaO, MgO,
Although a small amount of ZrO ₂ stabilizing element such as Y ₂ O ₃ is contained, it is treated here as the number of metal oxide components.

[0013]

[Example] While supplying molten stainless steel having a composition of SUS304 and a temperature of 1500 ° C. to the pool 3 of the twin-drum continuous casting machine shown in FIG. 1, a thin metal film having a thickness of 3.5 mm and a plate width of 1330 mm is used. The strip was cast at a casting speed of 50 m / min for about 3 hours. The scum weir 6 has a thickness of 8 mm, and Tables 1 and 2 show the composition, particle size, physical characteristics, cracking of the scum weir during casting, melt loss index, and cast slab defect index. It is preferable that both the melt loss index and the defect index are small, and 2 or less is a pass. Also,
If a crack occurs during casting, casting is discontinued, so neither the melt loss index nor the defect index is listed.

[Table 1]

[Table 2]

[0014]

As described in detail above, the present invention uses the graphite-metal oxide system which is excellent in heat shock resistance, corrosion resistance, strength and the like as the scum weir refractory, so By performing stable continuous casting operation for a long time while preventing the surface defects of the metal ribbon, it is possible to manufacture a slab with good quality, and it is more cost-effective than the conventional scum weir using BN. Can be reduced to 1/10 or less.

[Brief description of drawings]

FIG. 1 is a side sectional view of a main part of a twin-drum continuous casting machine.

[Explanation of symbols]

1 ... Cooling drum 2 ... Side weir 3 ... Hot water pool 4 ... Molten steel 5 ... Nozzle 6 ... scum weir S ... Metal ribbon R ... Meniscus

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tadashi Ikemoto             20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel shares             Company Technology Development Division F-term (reference) 4E004 DA13 RA04                 4G030 AA07 AA08 AA12 AA17 AA36                       AA46 AA47 AA60 AA63 AA64                       BA27                 4G031 AA03 AA04 AA08 AA12 AA29                       AA37 AA39 BA25

Claims (4)

[Claims] 1. An apparatus for casting a thin metal strip while supplying molten steel to a molten metal pool formed by a pair of cooling drums and a pair of side dams, wherein the molten metal is distributed along the width direction of the cooling drum. A pair of scum weirs provided, wherein the scum weir comprises 3 to 15 mass% graphite and 60 to 90 mass% metal oxide as main components. Machine scum weir. 2. The graphite has a maximum particle size of 300 μm or less,
The scum weir of the twin-drum continuous casting machine according to claim 1, wherein the average particle diameter is 100 µm or less, the maximum particle diameter of the metal oxide is 100 µm or less, and the average particle diameter is 50 µm or less. 3. The main component of the metal oxide is ZrO ₂ , A
The scum weir of the twin-drum continuous casting machine according to claim 1 or 2, wherein the scum weir is 1 type or 2 types of l ₂ O ₃ . 4. An apparatus for casting a metal strip while supplying molten steel to a molten metal pool formed by a pair of cooling drums and a pair of side dams, wherein the molten metal is distributed along the width direction of the cooling drum. A pair of scum weirs provided, wherein the scum weir has a bending strength of 12 MPa or more and a thermal expansion coefficient of 7 × 1.
A scum weir for a twin-drum continuous casting machine, which has a thermal conductivity of 0 to ^-6 (1 / ° C) or less and 3 to 15 W / mK.