JPH06182500A - Casting nozzle for twin belt type continuous caster - Google Patents

Abstract

PURPOSE:To restrain molten steel flow just below a nozzle in a mold, to uniformize flow speed of the molten steel in the width direction and to prevent the longitudinal crack in a cast strip by forming the discharging hole width in the thickness direction of the nozzle to a tapered shape gradually narrowed and the center inner part of the nozzle to the divided flow structure with a partitioned wall in the thickness direction of the nozzle. CONSTITUTION:On the upper surface of the nozzle, a sprue part 2 and a nozzle pouring hole 1 from a tundish are provided, and ordinarily, the tundish nozzle is fitted to the pouring hole 1 to pour the molten metal. A pouring part 3 in the nozzle body is divided with the partitioned wall 4 so as to inject the molten metal into the mold. Further, the lower end of the nozzle is formed as arc-state in the corner part 5, and the discharging hole 8 in the nozzle is formed as the tapered shape in the inner surface at the lower end part, and at the tip part 6 of the nozzle, the discharging hole having narrow width is formed. Such a nozzle forms the uniform molten steel flow pattern in molten steel flow speed, solidified shell thickness and solidified thickness, and the uniform shell is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of the discharge flow of a flat nozzle used in the production of thin plate cast pieces by a twin belt type continuous casting machine.

[0002]

2. Description of the Related Art A twin-belt type continuous casting machine has a flat slab with a flat or rectangular shape, and because of its thin wall, the rolling process can be omitted, which is advantageous in terms of process saving and energy saving. The actual machine is being considered. However, since the casting nozzle is a flat tubular flat nozzle, it has a smaller volume than a normal nozzle, and the uneven flow of molten steel in the mold has a large effect, causing vertical surface cracks in the product. It tends to be easy. The shape of the nozzle used for this thin cast piece is generally a thin and flat shape of the mold, so that the thickness of the nozzle is often a thin and flat tubular shape correspondingly.

In this conventional nozzle, the flow velocity of the molten steel just below the nozzle tends to be higher than the flow velocity of the side portion thereof,
This high-velocity molten steel flow acts as a discharge jet to attack the shell and promote stress concentration in the thin shell region. This action and other factors, such as the restraint condition due to the friction of the belt, often lead to the occurrence of vertical cracks in the slab. In order to prevent this slab vertical cracking, the shape of the nozzle has not been sufficiently investigated. Improvement of belt lubrication has been taken as a typical prevention of vertical slab cracking. However, as a more important factor, it has become necessary to study the improvement of the flow of molten steel discharged from the nozzle in order to prevent the local thin shell region from being generated due to the shape of the nozzle. Regarding the nozzle of the belt type continuous casting machine, for example, JP-A-4-37446 discloses that the nozzle is tapered in the thickness direction in order to prevent the deposit of the nozzle and stabilize the operation. However, there is no disclosure regarding vertical slab prevention. In the field of twin-belt continuous casting machines, the slab quality and nozzle shape have hitherto been pointed out as problems in preventing vertical slab cracking.

[0004]

DISCLOSURE OF THE INVENTION The present invention prevents the above-mentioned problem, that is, stress concentration which tends to occur in a thin shell due to shell attack in a flat mold of a twin belt type continuous casting machine in high speed casting. It was made for the purpose of doing. That is, depending on the shape of the nozzle, the molten steel flow directly below the nozzle in the mold is suppressed, local concentration of the molten steel flow is avoided, the flow velocity in the width direction of the mold is made uniform, and the flow velocity distribution for preventing vertical slab cracking is created. The present invention provides a belt type continuous casting machine nozzle that realizes, that is, makes the initial solidification process uniform and realizes stable casting with a constant shell thickness.

[0005]

Means for Solving the Problems The present invention is to solve the above problems, and the gist thereof is to provide a nozzle for a thin plate continuous casting having a flat cylindrical flat type cross section over a predetermined length. The shape of the corner portion is a uniform circular arc in the thickness direction of the nozzle, and the nozzle discharge holes are formed by the tapered inner surfaces which are continuously continuous from the flat portion toward the tip and which are opposed to each other. The shape of the hole is a smooth curved surface downward from the arc-shaped corner to the center, and the discharge hole width in the nozzle thickness direction is asymptotically narrowed. The nozzle for a twin-belt continuous casting machine is characterized by having a flow dividing structure with partition walls in the vertical direction.

That is, in the current straight nozzle,
There is a tendency for the shell thickness to become thinner immediately below the nozzle.This is because the growth of the shell due to belt cooling, where the molten steel flow velocity is large immediately below the nozzle, is washed by this nozzle jet and the shell is attacked. The slab becomes vertical crack. From this point of view, the present invention provides a nozzle in which the nozzle jet has an arcuate opening on both sides of the lower end and a throttle shape at the center. In the present invention, the jet flow discharged from the nozzle is widened into a film-like flow over the entire width direction of the mold while ensuring a full flow in the nozzle, so that there is no local concentration of flow as in the prior art. Further, in the present invention, the total cross-sectional area of the discharge jet is not changed so much in order to secure the casting speed.
Also, in widening the nozzle, in order to widen in the side direction,
It is also necessary to provide openings on the sides. For this reason, an opening is provided from the corner of the tip, and the opening is provided on the entire nozzle tip surface. Furthermore, in order to obtain a stable radial jet jet, the tip of the nozzle is arcuate. Further, in the nozzle of the present invention, a partition wall is formed in the inner central portion of the injection portion in the depth direction to form a shunt type, so that the flow velocity immediately below the nozzle jet flow is further reduced and the jet flow that spreads to the left and right is It can be made uniform and contributes to uniform shell formation. The operation and effect will be described in more detail below based on an embodiment of the present invention.

[0007]

EXAMPLE FIG. 4 is a conceptual diagram during casting by a belt type continuous casting machine. Belt type continuous casting machine, tundish 1
The molten steel 11 of 0 passes through the upper nozzle 12, the sliding nozzle 13 and the lower nozzle 14 of the tundish and is injected into the flat nozzle 15, and the molten steel flow velocity 16 is jetted into the mold in a branched state as shown in the figure. FIG. 1 is a (a) plan view, (b) front view, (c) side view and (d) bottom view of a nozzle according to the present invention. As shown in FIG. 1, there is a sprue part 2 from a tundish and a nozzle injection port 1 on the upper surface of the nozzle, and usually a tundish nozzle is inserted into the injection port 1 to inject molten steel. The pouring part 3 of the nozzle body is divided by the partition wall 4 and jetted into the mold. The lower end of the nozzle has a corner portion 5 in an arc shape, and the nozzle discharge hole 8 has a tapered inner surface at the lower end portion, and a narrow discharge hole is formed at the nozzle tip 6.

As shown in the bottom view, the discharge hole at the tip of the nozzle normally has two discharge holes 9 for diverting. Figure 2
2 is a schematic view of a nozzle of the present invention of a type different from that of FIG.
In FIG. 2, the arcuate shape of the corner portion of the nozzle tip is cut into the central portion of the nozzle, and there is also one discharge hole. In this shape, the discharge hole width at both ends is 1 at the central portion. The degree of narrowing has become large as / 2 or less. In this embodiment, the width of the discharge hole is about 10 m at both ends.
m is about 4 mm at the central part, but this value is determined by the operating conditions of the belt type continuous casting machine.

FIG. 3 shows (a) molten steel flow rate, (b) solidification shell thickness, and (c) solidification when an actual casting test was conducted using the nozzle of the embodiment of the present invention and the conventional straight nozzle. It is a figure which measured and compared the nonuniformity. As shown in FIG. 3 (a), in the relationship between the distance from the center of the mold width and the molten steel flow velocity, the round nozzle of the present invention has a small difference due to the distance from the center of the mold width, and has a variation compared to the conventional straight type. Is good. Further, in the solidified shell thickness (b), the nozzle of the present invention also shows extremely improved results. In particular, in the solidification nonuniformity (c), which greatly affects the quality, the round nozzle of the present invention shows remarkably good results as compared with other conventional straight nozzles.
As described above, the nozzle of the present invention shows a uniform molten steel flow pattern in the molten steel flow rate, the solidified shell thickness, and the solidified shell thickness as compared with the straight type, and it is understood that the shell is highly uniform. That is, it can be seen that the nozzle of the present invention has a particularly large effect in preventing vertical cracking of the cast slab by making the solidified shell thickness of the belt type continuous casting machine uniform.

[0010]

According to the present invention, the flow velocity immediately below the nozzle is suppressed, the flow velocity of molten steel in the width direction is made uniform, and the initial solidification is made uniform, whereby vertical cracks on the surface of the slab are prevented and the belt type It is of great industrial significance that the casting operation is stabilized and the quality is improved by the continuous casting machine.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, in which FIG.
(B) Front view, (c) Side view, (d) is view A of (c)
It is a cross-sectional view from -A.

FIG. 2 is an enlarged view of FIG.

FIG. 3 (a) Molten steel flow velocity in an embodiment of the present invention,
It is a figure which shows the relationship between the solidification shell thickness, (c) solidification nonuniformity, and the distance from the mold width center.

FIG. 4 is a conceptual diagram showing a casting situation of a belt type continuous casting machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Injection port 2 ... Gate part 3 ... Molten part 4 ... Partition wall 5 ... Corner part 6 ... Nozzle tip 7 ... Gate part inclined part 8 ... Discharge hole inner surface 9 ... Discharge hole appearance 10 ... Tundish 11 ... Molten steel 12 ... Upper nozzle 13 ... Sliding nozzle 14 ... Lower nozzle 15 ... Flat nozzle 16 ... Molten steel jet

Front page continuation (72) Inventor Junichi Nakagawa, Oita City, Oita Prefecture, 1 oaza Nishinosu Nippon Steel Co., Ltd. Oita Steel Works (72) Inventor Shinji Namie, Oita City, Oita City 1 Nishinozu Nippon Steel Co., Ltd. Inside the Oita Works (72) Inventor Masao Shimizu 1 Nishinosu, Oita-shi, Oita Shin Nippon Steel Co., Ltd. Inside the Oita Works (72) Toru Takahashi 1st Nishinozu, Oita-shi, Oita Pref. Company Oita Works (72) Inventor Tomoaki Hagiwara No. 1 Nishinosu, Oita City, Oita Prefecture Shin Nippon Steel Co., Ltd. Oita Works (72) Inventor Hiroshi Nakajima 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture (72) Inventor Junkichi Yoneda 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Works

Claims (1)

[Claims] 1. A thin plate continuous casting nozzle having a flat tubular flat type whose cross section extends over a predetermined length, wherein the nozzle tip portions are smoothly continuous from the flat portion toward the tip, and face each other with a taper. The nozzle discharge hole is formed by the inner surface of the nozzle discharge hole, and the shape of the nozzle discharge hole is a curved surface that is smooth downward from the arc-shaped corner portion to the center portion, and the discharge hole width in the nozzle thickness direction is asymptotic. A twin-belt continuous casting machine nozzle characterized by having a narrowing hourglass shape and having a flow dividing structure with a partition wall in the nozzle depth direction inside the center of the nozzle.