JP5723044B1 - Tundish nozzle for continuous casting of steel and continuous casting method - Google Patents

Abstract

Provided is a tundish nozzle that solves the problem of nozzle clogging and facilitates continuous casting of an Al deoxidized steel billet. An installation part of an inclined fully-open nozzle 7 which is normally used for continuous casting of a billet is moved from a bottom surface of a tundish to a lower part of a bottom plate of a tundish through a cylindrical nozzle 3, and the part is heated to a high temperature. maintain. As a heating method, an induction heating coil 10 is disposed concentrically on the outer periphery of the cylindrical nozzle 3 to inductively heat the cylindrical graphite 9, and the cylindrical graphite 9 is radiatively heated. Alternatively, the cylindrical nozzle 3 is directly induction heated as a conductive refractory. By increasing the temperature of the fully-open nozzle 7, the adhesion of alumina or the like in the bottleneck 8 accompanying Al deoxidation is suppressed, and a corrosion reaction is induced. Al deoxidized steel can be cast easily without requiring a flow control mechanism such as a sliding gate. [Selection] Figure 1

Description

  The present invention relates to a tundish nozzle used in continuous casting of steel.

  In the continuous casting of steel, the molten steel in the ladle after refining is poured into a tundish, adjusted to a predetermined temperature, and continuously cast into a mold at a predetermined flow rate through a refractory tundish nozzle. The outer slab of the slab is formed with a mold, and the slab is manufactured through cooling and solidification.

There are three methods for adjusting the casting flow rate. In general, a stopper nozzle method or a sliding gate method is employed for casting a slab or bloom having a large flow rate.
In the former, a larger nozzle diameter is set for a predetermined flow rate, and a spherical stopper head is made to approach the upper curved surface of the nozzle that expands in a trumpet shape to form a ring-shaped bottleneck. Adjust.
In the latter, three perforated refractory plates are connected to the lower surface of the nozzle so that the holes are in series with the nozzle holes, and the intermediate plate is slid to form a bottleneck and adjust.
A billet with a small flow rate usually employs a fully open nozzle system. A fully open nozzle is a nozzle that has a hole that inclines and shrinks downward, has a bottleneck formed on the bottom surface, and always flows out in a fully open state. It is characterized by less turbulence in the outflow. The flow rate depends on the bottom cross-sectional area and the molten steel depth (constant at normal time). Accordingly, the nozzle diameter is uniquely set for a predetermined flow rate.
There are no structures or flow rate adjusting mechanisms that affect the flow rate above and below the nozzle.

  The advantage of the fully open nozzle method is that the refractory cost is low. Nozzle, which is a high-grade refractory, has a small unit weight, good durability, and less turbulence in the falling flow, so an auxiliary refractory such as an immersion nozzle is unnecessary and only one is sufficient. In other systems, it is indispensable to connect an immersion nozzle in which the lower end is immersed in the molten steel in the mold because of the turbulence of the falling flow. Necessary number of refractories is 3-5, cost increases several times due to increase in unit weight, decrease in durability (determined by the weakest part), and the like.

On the other hand, when Al deoxidized steel is cast, deposits accumulate on the inner surface of the nozzle and casting becomes impossible as soon as possible. This is a so-called nozzle blockage problem. The problem is most troublesome with this method.
Various studies have been made on the mechanism of occlusion, but it has not yet been solved. Not only simple adhesion of alumina, alteration of refractory surface layer, reaction of refractory with Al and alumina in molten steel, influence of FeO generated by reoxidation in tundish, formation and deposition of iron particles and layers, Nozzle temperature and temperature gradient are complicated.

  Accumulation occurs not only in the bottleneck but also on the inner surface of the immersion nozzle below the bottleneck. Strangely, there is little accumulation above and is not debated. Perhaps the deposits drift and pass through the Kushiro. Although there are some countermeasures, a method that seems to be related to the present invention is examined.

  In Patent Document 1, regarding the adhesion problem of Al deoxidized steel, the adhesion to the immersion nozzle below the Kushiro sliding gate is suppressed by maintaining the nozzle at a high temperature. It is disclosed that a conductive refractory is buried inside and high-frequency induction heating is performed from the periphery. In addition to the metallurgical effect, it is emphasized that there is no leakage to molten steel and equipment due to induction.

The problem with this method is the refractory cost, which is that the expensive immersion nozzle becomes more complicated and expensive, and becomes more expensive due to lower durability.
Another problem is that the conventional fully open nozzle is provided at the bottom of the tundish, so that this method cannot be applied.

Patent Document 2 discloses a method that solves the problems of the method and makes it easy to use.
According to this, radiation heating is performed by a heater lined with a heat insulating member on the outer periphery of the immersion nozzle. Accumulation of deposits is suppressed, the existing immersion nozzle can be used as it is, and the heater is split, making it easy to attach and detach.
It is difficult to apply this method to a fully open nozzle as in the above method.

Other examples of suppressing adhesion deposition will be given. Casting can be continued by adding Ca to Al deoxidized steel after addition of Al in molten steel and modifying the easily-adhesive alumina to a low melting point compound.
Although effective, adhesion is not completely eliminated. With a fully open nozzle, the flow rate decreases even with a small amount of adhesion, and the adhering material wraps around the lower surface of the nozzle and disturbs the casting flow, resulting in insufficient casting time. The stopper nozzle method and sliding gate method are sufficiently effective.

  As a method of casting Al deoxidized steel in a billet with a small cross section, there is often a method in which Al wire is continuously added in the mold, but it is only in low grade steel due to lack of uniformity and frequent occurrence of alumina inclusions. Not applicable.

Published Patent Publication 2002-336842 Published Patent Publication 2010-167495

  In continuous casting of Al deoxidized steel, Al compounds and the like are deposited on the inner surface of the nozzle. In the case of casting by the fully open nozzle method, the nozzle is easily closed early. This invention makes it a subject to solve the said nozzle obstruction | occlusion problem in a fully open nozzle system, and provides an effective tundish nozzle and an effective casting method.

  A first invention is a tundish nozzle for continuous casting provided for casting molten steel in a tundish into a mold. 1) An upper end is located at a tundish bottom and a lower end passes through a tundish iron bottom plate and is downward. It consists of a protruding cylindrical nozzle and a fully-open nozzle with a downwardly inclined hole provided inside the cylindrical nozzle. 2) The minimum diameter of the fully-open nozzle is set corresponding to a predetermined flow rate in a predetermined molten steel head 3) A tundish nozzle characterized in that the periphery of the fully open nozzle is heated and maintained at a high temperature from a high frequency induction heating coil provided concentrically with a gap around the outer periphery of the cylindrical nozzle.

  In the second invention, the lower end of the cylindrical nozzle is stopped on the mold, the cylindrical graphite is provided between the induction heating coil and the cylindrical nozzle, the cylindrical graphite is induction-heated, and the high-temperature cylindrical graphite The tundish nozzle according to the first invention, wherein the periphery is radiantly heated.

  A third invention is the tundish nozzle described in the second invention, characterized in that a dip tube whose lower end is immersed in molten steel in a mold is hermetically connected to the lower end of the cylindrical nozzle.

  A fourth invention is the tundish nozzle described in the first invention, characterized in that the lower end of the cylindrical nozzle is immersed in molten steel in the mold, the material is conductive, and the periphery of the fully opened nozzle is directly induction heated. It is.

  A fifth invention is a continuous casting method in which molten steel in a tundish is cast into a mold through a fully-open nozzle having a hole that slopes down and down. A high-frequency induction heating provided inside a cylindrical nozzle protruding in a concentric manner with a minimum diameter of the fully opened nozzle corresponding to a predetermined flow rate in a predetermined molten steel head and having a gap around the outer periphery of the cylindrical nozzle The continuous casting method is characterized in that the periphery of the fully open nozzle is heated from the coil and maintained at a high temperature.

  The first effect of the above invention is that when casting Al deoxidized steel, the refractory in the bottleneck part is maintained at a high temperature by induction heating. 1) Adhesion deposition of alumina or the like in the bottleneck is extremely reduced, 2) Corrosion may also occur depending on the refractory material. Continuous casting is maintained with appropriate heating input.

The second effect is, when casting the Al-deoxidized steel, the flow control mechanism such as a refractory costly stopper nozzle Toka sliding gate is not required, only relatively simple composite nozzle consisting of a cylindrical nozzle fully open nozzle Therefore, the refractory cost is greatly reduced. In the case of indirect heating by radiation, the cylindrical nozzle can be replaced with an ordinary lower refractory instead of an expensive conductive refractory, which is further reduced.

  The third effect is that nozzle clogging occurs when the casting temperature is too low irrespective of the deoxidation method. In order to prevent this, the refining end temperature is usually set higher. In the nozzle of the present invention, clogging hardly occurs. The refining temperature is induced to a low level, which helps to save energy.

It is a conceptual diagram of the prototype of this invention. It is a conceptual diagram of Example 2 of the present invention. It is a conceptual diagram of Example 3 of the present invention. It is a conceptual diagram of Example 4 of the present invention. It is a conceptual diagram of Example 5 of the present invention.

Hereinafter, embodiments will be described with reference to the drawings.
FIG. 1 illustrates a case where the prototype of the present invention is applied to a main casting part from a tundish to a mold.
A nozzle receiving brick 2 is provided on a tundish iron skin bottom plate 1, and a fully open nozzle is fitted on the nozzle receiving brick 2 in the conventional method, but in the present invention, a cylindrical nozzle 3 is inserted. The upper end is located at the bottom of the tundish, and the lower end 4 protrudes downward from the opening 5 provided in the iron bottom plate 1 and upward from the mold 6. The cylindrical nozzle 3 is internally provided with a fully-open nozzle 7 having a hole that is inclined and reduced downward. A narrow path 8 is formed on the lower surface of the nozzle 7.
A cylindrical graphite 9 heating element is concentrically disposed on the outer periphery of the cylindrical nozzle 3, and a high-frequency induction heating coil 10 is disposed on the outer periphery.

At the time of casting, the induction heating coil 10 is energized several tens of minutes before the heating element of the cylindrical graphite 9 is heated, and the cylindrical nozzle 3 and the fully opened nozzle 7 inside are sufficiently preheated by radiation heating from the heating element. The upper opening of the cylindrical nozzle is closed with a lid of a mild steel plate having a thickness of several mm. By the time the molten steel poured into the tundish from the ladle reaches a predetermined depth, the lid is melted and vigorously cast into the mold. Since the area around the Kushiro is sufficiently hot, there is no blockage due to the adhesion of molten steel. After the predetermined depth is maintained.
The cast-in flow is the same as the outflow flow of the fully-open nozzle that is often used for billets, and the turbulence is small, and falls into the center of the narrow mold opening.
Even if the molten steel becomes excessively low in temperature, the nozzle does not clog and solidify, so that the refining temperature can be lowered.

The casting flow rate is obtained by the following formula, and the minimum diameter of the fully opened nozzle is uniquely determined corresponding to the predetermined flow rate.
W = ρ · V · π · d 2/4
V = √ (2gh)
W: Casting flow rate (kg / s), ρ: Molten steel density (kg / m ³ ), V: Kushiro flow velocity (m / s),
d: Nozzle minimum diameter (m), g: acceleration of gravity (0.98 m / s ² ),
h: Molten steel head (depth from the molten steel surface in the tundish to the bottleneck) (m)
When casting 100-200 mm square billets, the casting efficiency is usually in the range of 10-30 t / h, the molten steel head is in the range of 500-800 mm, and the inner diameter (minimum part) of the fully-open nozzle used is 13-20 mm. It is. In the present invention, since the nozzle moves downward, the molten steel head is increased by 200 to 500 mm. It is necessary to correct the nozzle diameter accordingly.

  The inner diameter of the cylindrical nozzle is preferably 3 to 6 times the inner diameter of the fully open nozzle. If the flow rate is less than 3 times, the splash flow adheres to the inner surface of the cylindrical nozzle and grows, and the flow falls to the mold edge. If it is 6 times or more, the waste of the refractory increases.

From the above-mentioned literature, adhesion and deposition of alumina and the like are suppressed by high temperature heating of the nozzle in casting of Al deoxidized steel, but it is not zero. Since the tundish nozzle of the present invention uses a fully open nozzle, the influence of adhesion is great. As a countermeasure, conventional addition of Ca is performed.
Although the adhesion proceeds, a part of the refractory is semi-molten by the action of Ca. The refractory surface layer also reacts with the adhering substance to lower the melting point and become semi-molten and easily corroded together. It is known that both pore shrinkage due to adhesion and expansion due to corrosion are in progress. Usually adhesion is better. Some adhesion can be withstood by the stopper nozzle method, but the full-open nozzle method has an influence on the flow rate and cannot withstand for a long time.

  In the present invention, the entire periphery of the fully open nozzle is maintained at a high temperature, for example, 1500 ° C. or higher, which is close to the molten steel temperature. As a result, solidified iron that acts on the deposits of deposits does not first adhere. Deposits are difficult to grow. The refractory surface layer is semi-melted and easily corroded. Depending on conditions, corrosion is better. It becomes easy to balance by the heating conditions of the nozzle and the conditions of the Ca treatment.

  FIG. 2 shows a second embodiment. A dip tube 11 that is newly immersed in the molten steel 12 in the mold is hermetically connected to the lower end 4 of the cylindrical nozzle 3 using the structure shown in FIG. Ordinary immersion nozzle and powder casting may be performed, or oil lubrication casting may be performed. It should be noted that the dip tube 11 is filled with molten steel by making it airtight, and the molten steel head has a depth from the molten steel surface in the tundish to the molten steel surface in the mold.

  In this casting method, a high-grade refractory is required for the fully-open nozzle and the immersion nozzle as before, but both have a small mass and are cost-effective. As the cylindrical nozzle, an intermediate class such as a chamotte type can be used, which is also cost-effective.

FIG. 3 shows a third embodiment. In the original mold of FIG. 1, the lower end of the cylindrical nozzle 3 is immersed in the molten steel 12 in the mold. A commercially available immersion nozzle is suitable. The material is graphite alumina. Alumina contains 5 to 15% of graphite, and a specific resistance (about 0.01 Ωcm) close to that of graphite (about 0.001 Ωcm) is obtained. It has electrical conductivity and can be easily induction heated directly.
In this method, the fully opened nozzle portion is heated quickly.

  FIG. 4 shows a fourth embodiment. The cylindrical nozzle 3 is divided into upper and lower parts. The lower end of the upper nozzle 31 is stopped just below the bottom plate, and the lower nozzle 32 is directly heated from an induction coil by connecting a general graphite alumina submerged nozzle in an airtight manner. Except for the fully open nozzle, it is the same as a normal heated immersion nozzle.

FIG. 5 shows a fifth embodiment. In method 3, the material of the fully open nozzle is the same as that of the cylindrical nozzle 3 and is integrally formed. Extending the minimum diameter part of the fully open nozzle to a throat makes it durable against corrosion.
It may be easy to balance adhesion / deposition and corrosion.

  The present invention can be easily applied to existing continuous casting for billets.

1: Iron skin bottom plate 2: Nozzle receiving brick 3: Cylindrical nozzle 4: Lower end 5: Iron skin opening 6: Mold 7: Fully opened nozzle 8: Kushiro 9: Cylindrical graphite 10: Induction heating coil 11: Dip tube 12: Molten steel in mold 31: Upper nozzle 32: Lower nozzle 41: Fully open nozzle

Claims (4)

  A tundish nozzle for continuous casting provided for casting molten steel in a tundish into a mold, 1) a cylindrical nozzle whose upper end is located at the tundish bottom and whose lower end passes through the tundish iron bottom plate and projects downward The cylindrical nozzle comprises a fully open nozzle provided in the projecting part and having a downwardly inclined hole. 2) The flow control mechanism of either a stopper or a sliding gate is provided above and below the fully open nozzle. The flow rate is set by the fully open nozzle itself, and 3) resistance heating element cylindrical graphite is provided on the outer periphery of the cylindrical nozzle so that the fully open nozzle is maintained at a high temperature, and an induction heating coil is provided on the outer periphery. Tundish nozzle characterized by   A tundish nozzle for continuous casting provided for casting molten steel in a tundish into a mold, 1) a cylindrical nozzle whose upper end is located at the tundish bottom and whose lower end passes through the tundish iron bottom plate and projects downward And a fully open nozzle provided in the projecting portion of the cylindrical nozzle and having a downwardly inclined hole. 2) A flow rate adjusting mechanism of either a stopper or a sliding gate above and below the fully open nozzle. 3) The material of the cylindrical nozzle is graphite alumina with a graphite content (mass%) of 5% or more and 15% or less at least in the protruding portion. 4) A tundish nozzle characterized in that an induction heating coil is provided on the outer periphery of the cylindrical nozzle so that the fully open nozzle is maintained at a high temperature.   The tundish nozzle according to claim 1 or 2, wherein the shape of the fully open nozzle is extended by adding a parallel portion having the same diameter in the flow direction at the lower end where the hole diameter is minimum.   In a continuous casting method in which molten steel in the tundish is cast into the mold through a fully-open nozzle having a hole that tilts downward, the cylindrical nozzle that protrudes downward through the fully-open nozzle at the bottom of the tundish and the lower end through the tundish iron bottom Provided inside the protruding part, the flow rate is set by the fully open nozzle itself without having a flow rate adjusting mechanism of either a stopper or a sliding gate above and below the fully open nozzle, and there is a gap on the outer periphery of the cylindrical nozzle. A continuous casting method characterized in that the periphery of the fully open nozzle is heated and maintained at a high temperature by a high frequency induction heating coil provided concentrically.

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