JP2001198655A - Immersed nozzle for continuous casting, and continuous casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an immersed nozzle for continuous casting having the minimum inside radius which does not causes clogging of the nozzle. SOLUTION: The inside radius r of the nozzle satisfies the inequality 1: r>Ca×Q1/3×t1/3, where Ca is a constant, and calculated from the inequality 1 by measuring Q and t using another nozzle of different inside radius, and different according to the kind of steel, for example, 29.2 for low-carbon steel, medium-carbon steel and high-carbon steel, and 34.7 for super-low carbon steel, stainless steel and alloy steel, Q is the flow rate t/m of the molten steel passing through the nozzle, and t is the time of use of the nozzle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting immersion nozzle and a continuous casting operation method using the nozzle.

[0002]

2. Description of the Related Art In this type of immersion nozzle for continuous casting, the amount of oxides included in molten steel adheres to and accumulates on the inner surface of the immersion nozzle, causing fluctuations in the injection amount. Had an effect. Various attempts have been made to prevent variations in the injection volume. Of these, it is known that the larger the inner diameter of the nozzle, the smaller the change in the injection amount due to nozzle blockage, but the larger the inner diameter of the nozzle,
The outer diameter is inevitably large, and in the case of the immersion nozzle, the gap between the nozzle and the mold is reduced. As a result, the molten steel between the nozzle and the mold was supercooled, and the inflow of the artificial slag was poor, and the surface of the slab was sometimes flawed. For this reason, it is desirable that the inside diameter of the nozzle be as small as possible within a range that can prevent the fluctuation of the injection amount due to the blockage. However, a method for obtaining the minimum value of the nozzle inner diameter that does not cause the fluctuation of the injection amount has been hitherto known. Therefore, when remodeling or installing a continuous casting machine, or when expanding the injection flow rate or the use time of the nozzle, in order to find the minimum value of the nozzle inner diameter that does not cause a change in the injection amount, an experiment was performed each time. Was repeatedly performed.

As a technique for preventing nozzle blockage, for example, Japanese Unexamined Patent Publication No. 9-241404 discloses an immersion for continuous casting in which one or more steps are formed in a nozzle inner hole in order to prevent nozzle blockage due to alumina adhesion. In the nozzle, at least a part of the inner hole portion in contact with the molten steel is made of a refractory material having a carbon content of 5% by weight or less, and a stepped continuous hole defining a minimum inner diameter of a portion having no step structure of the inner hole portion with respect to the amount of molten steel passed. An immersion nozzle for casting is introduced.

[0004]

However, the conventional continuous immersion nozzle for continuous casting has a minimum inner diameter specified as disclosed in Japanese Patent Application Laid-Open No. 9-241404. The inner diameter is determined by trial and error as described above. However, the method does not consider the growth of deposits on the inner diameter of the nozzle, which varies depending on the type of steel and the casting speed.

In a continuous casting operation using an immersion nozzle, an abnormality occurs due to nozzle blockage due to deposits. (No abnormality can be confirmed during the operation. It is determined that there is an abnormality), but it is necessary to stop casting continuously. Therefore, the production efficiency has been reduced, and there has been a long-awaited need for an ethical determination of the number of possible castings for the immersion nozzle.

Therefore, the invention according to claim 1 of the present invention ethically determines the minimum required immersion nozzle inner diameter for slabs of different steel types to be continuously cast, and reduces the planned casting speed and the number of continuous castings. It is an object to provide a continuous casting immersion nozzle which can be maximized without nozzle blockage.
In the continuous casting operation using the immersion nozzle, the invention described in claim 2 ethically obtains the casting available time until the immersion nozzle is closed, so that the nozzle clogging trouble occurs during the planned number of continuous castings. It is an object of the present invention to provide a continuous casting operation method capable of preventing the above.

[0007]

The invention according to claim 1 relates to a continuous casting immersion nozzle which achieves the first object, and is obtained from a casting speed and a continuous casting time of a slab to be cast by a continuous casting machine. The flow rate of the molten steel passing through the nozzle and the usage time of the nozzle satisfy the following equation (1).

[0008]

Φ> Ca × Q ^1/3 × t ^1/3 where Ca is a constant, and the casting target steel type is 29.2 for low carbon steel, medium carbon steel, and high carbon steel, and extremely low carbon steel. , 34.7 for stainless steel and alloy steel. In addition, Φ: nozzle inner diameter (mm) Q: flow rate of molten steel passing through the nozzle (t / min) t: service time of the nozzle (hr) According to the present invention, for molten steel for continuous casting of different steel types, The required minimum inner diameter of the immersion nozzle can be designed and planned from the planned continuous casting speed and the number of continuous castings, so that the immersion nozzle manufacturing efficiency can be increased and the immersion nozzle can be prevented from having trouble during casting.

Further, the invention according to claim 2 relates to a continuous casting operation method for achieving the second object, wherein the following formula 2 is used when performing continuous casting using a continuous casting immersion nozzle having a predetermined nozzle inner diameter. The casting is performed by continuously determining the number of castings by using or replacing the immersion nozzle so as to satisfy the formula.

[0010]

T <Φ ³ / (Ca ³ × Q) Here, Ca is a constant, and the casting target steel type is 29.2 for low carbon steel, medium carbon steel, and high carbon steel, and extremely low carbon steel and stainless steel. For steel and alloy steel, it is 34.7. In addition, Φ: Nozzle inner diameter (mm) Q: Flow rate of molten steel passing through the nozzle (t / min) t: Continuously medium time or nozzle use time (hr) According to the present invention, use of the nozzle for the corresponding nozzle inner diameter The casting time can be obtained by dividing the casting time by the average casting speed, so that the number of castings can be obtained one after another. This has the effect.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention has been devised by the present inventors in the process of predicting a logical trouble in consideration of troubles such as nozzle clogging and abnormal quality in a continuous casting operation and can be sufficiently applied to an actual operation. Equation 1 is based on the following technical idea. The change in inner diameter due to deposits on the nozzle is proportional to the flow rate of molten steel passing through the nozzle, the concentration of oxide-based inclusions in the molten steel, and inversely proportional to the nozzle cross-sectional area. When the inner diameter change rate is arranged, the following equation 3 is obtained.

[0012]

DΦ / dt = −K × Q × C / (π × Φ ² ) where Φ; nozzle inner diameter t; nozzle use time K; constant including nozzle shape and other factors Q; Flow rate of molten steel C: concentration of oxide-based inclusions in molten steel.

## EQU3 ## Next, when dt is rearranged on the left side of Expression 3 and Φ is integrated in order to obtain a time for a change in inner diameter,

[0014]

## EQU4 ## t = -π / (3 × K × Q × C) × Φ ³ is obtained.

[0015]

Φ = − [(3 · K · C) / π] ^1/3 × Q ^1/3 × t ^1/3 The above equation (5) logically represents the reduction in the nozzle inner diameter due to the concentration C of the oxide-based inclusions in the molten steel of the steel type to be cast, the flow rate Q of the molten steel passing through the nozzle, and the usage time t of the nozzle. It can be used by obtaining the initial nozzle inner diameter of the immersion nozzle for casting, and the relationship between the casting available time and the flow rate of molten steel when using an immersion nozzle having a certain inner diameter.

According to the present invention,-[(3 · K ·
C) / π] ^1/3 is replaced by a constant Ca.
a is Q using a nozzle with a different inside diameter,
And t can be calculated. That is, using a nozzle having a predetermined inner diameter, actual casting is performed at a predetermined molten steel flow rate Q, and the time when the tundish surface level changes (quality abnormality occurrence time) is measured. Therefore, Ca can be calculated backward.

Therefore, in carrying out the present invention, the flow rate Q of molten steel passing through the nozzle = the cross-sectional area of the mold from the predetermined maximum casting speed and order or production lot size according to the type of steel to be cast. × Maximum casting speed × Specific gravity of molten steel, nozzle use time t = Production lot size / (Molten steel flow rate × Number of molds) Calculate the right side of Equation 1 and continuously cast the nozzle inside diameter that satisfies Equation 1 of the present invention. The use of a immersion nozzle for use.

It is to be noted that, as a matter of course, the inner diameter of the nozzle is preferably as small as possible within a range in which nozzle blockage can be prevented.
In consideration of the above, when designing the immersion nozzle,
It is preferable to design the nozzle inner diameter by the formula.

[0019]

Φ = Ca × Q ^1/3 × t ^1/3 +10 Here, the constant Ca is 29.2 for low carbon steel, medium carbon steel, and high carbon steel for casting, and is an extremely low carbon steel. , 34.7 for stainless steel and alloy steel. The expression (2) according to the second aspect of the invention is obtained by rearranging the expression (1) according to the first aspect into t on the left side.

According to an embodiment of the present invention, when performing continuous casting using a continuous casting immersion nozzle having a predetermined nozzle inner diameter, the flow rate (passing through the nozzle) is determined from the maximum casting speed or the average casting speed of the casting steel type. The flow rate Q of the molten steel to be obtained = the cross-sectional area of the mold × the maximum casting speed × the specific gravity of the molten steel) is obtained, and the casting is performed by continuously determining the number of castings by using or replacing the immersion nozzle so as to satisfy the equation (2).

The constant Ca described in claims 1 and 2 differs depending on the nozzle shape and the like, and can be obtained by an empirical formula. Therefore, the constant Ca is not particularly limited. You may decide.

[0022]

[Experimental example] The flow rate Q of molten steel injected into the mold through the immersion nozzle is 1.275 t / min, and the casting time t is 3.75 Hr.
In the continuous casting machine, the inflow rate fluctuation (fluent level fluctuation) at the time of casting for the nozzle having an inner diameter of 55 mm satisfying the above equation (1) and the nozzle not satisfying the equation (1) having an inner diameter of 50 mm.
Was examined over time. The results are shown in FIG.

As shown in FIG. 1, the nozzle indicated by the dotted line which does not satisfy the equation (1) has a large variation in the injection amount with the passage of time, whereas the nozzle indicated by the solid line which satisfies the equation (1) has the injection amount. Fluctuation has been reduced.

[0024]

According to the present invention, since the inner diameter of the nozzle causing the nozzle blockage is obtained from Equation 1, the nozzle having the minimum nozzle inner diameter which does not cause the nozzle blockage can be obtained. Since the maximum casting time t of the nozzle can be obtained from equation (2), the cost can be reduced by maximizing the number of castings (how many times hot water can be received from a ladle with one tundish). It can be expected that the maximum number of continuous castings can be calculated backward when the casting speed is increased, so that the yield can be improved by reducing defective products, and the relationship between the flow rate Q passing through the nozzle of each steel type and the nozzle usage time t is understood. As a result, the production plan can be rationalized, and the loss of operation time can be reduced and the productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change with time of a molten metal level.

Claims (2)

[Claims] 1. A flow rate Q of molten steel passing through a nozzle and a use time t of the nozzle obtained from a casting speed and a continuous casting time of a slab to be cast by a continuous casting machine satisfy the following equation (1). Immersion nozzle for continuous casting. Φ> Ca × Q ^1/3 × t ^1/3 where Ca is a constant and the casting target steel type is 29.2 for low-carbon steel, medium-carbon steel and high-carbon steel, and extremely low-carbon steel , 34.7 for stainless steel and alloy steel. Also, Φ: Nozzle inner diameter (mm) Q: Flow rate of molten steel passing through the nozzle (t / min) t: Nozzle usage time (hr) 2. When performing continuous casting using a continuous casting immersion nozzle having a predetermined nozzle inner diameter, the immersion nozzle is used or replaced so as to satisfy the following equation (2), and the number of castings is continuously determined to perform casting. A continuous casting operation method characterized by the above-mentioned. T <Φ ³ / (Ca ³ × Q) Here, Ca is a constant, and the casting target steel type is 29.2 for low carbon steel, medium carbon steel, and high carbon steel, and extremely low carbon steel and stainless steel. For steel and alloy steel, it is 34.7. Also, Φ: Nozzle inner diameter (mm) Q: Flow rate of molten steel passing through the nozzle (t / min) t: Continuous time or nozzle use time (hr)