JPS59202143A - Prevention method of clogging of molten metal charging nozzle in continuous casting - Google Patents

Abstract

PURPOSE:To prevent surely clogging of a charging nozzle owing to solidification of a molten metal by impressing a voltage between the molten metal in a tundish and the molten metal in a casting mold and heating the molten metal in the charging nozzle. CONSTITUTION:The molten metal 2 in a tundish 1 is charged via a charging nozzle 4 into a casting mold 5, by which a billet is cast. An electrode 7 is immersed into the metal 6 in the mold 5 to provide a cathode, and an electrode 3 is immersed in the metal 2 in the tundish 1 to provide an anode. Electricity is conducted to said electrodes to pass the current from the electrode 3 through the nozzle 4 and the molten metal 8 in the charging nozzle to the electrode 7. The max. calorific value is thus obtd. in the nozzle 4 part to heat the nozzle 4 and the metal 8 by which the formation of the solidified metal and the clogging of the nozzle 4 are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing blockage of a nozzle for injecting molten metal into a mold in a continuous casting process for bath molten metal, such as molten steel.

Generally, when continuously casting molten metal, the nozzle for injecting the molten metal into the mold is attached to the bottom of the molten metal storage container (tundish), and in many cases, the tip of the nozzle is attached to the bath surface of the cast metal in the mold. It is immersed below.

Since the injection nozzle is cooled by contact with the outside air, the molten metal flowing through the injection nozzle solidifies, and the solidified metal grows to cause blockage of the injection nozzle (nozzle clogging). There is.

In recent years, continuous casting technology has diversified, and in particular, the process of obtaining extremely thin strips has become the focus.The injection nozzle in this case has an extremely large specific surface area, making it difficult to perform casting under conditions where the injection nozzle is easily clogged. I have to carry it out. Therefore, there is a strong demand for technology to prevent clogging of melt injection nozzles.

In response to such demands, various measures have been taken to prevent nozzle clogging, such as improving the material of the injection nozzle.

One of these techniques for preventing nozzle blockage is a device in which an induction heating device is fitted to the part of the injection nozzle that comes into contact with the outside air. That is, an induction heating coil is installed around the injection nozzle, and the eddy current generated in the molten metal inside the injection nozzle heats the molten metal inside the nozzle using t1 Joule heat, thereby preventing the nozzle from clogging due to solidification. .

However, a device having such a configuration requires an induction heating coil corresponding to a complicated injection nozzle shape and a device for cooling the induction heating coil, resulting in a problem that the device becomes complicated and large-scale.

Furthermore, in Japanese Patent Application Laid-Open No. 55-130364, a high-frequency current is applied to the molten steel passing through the molten steel injection nozzle, and the current is concentrated on the surface of the molten steel in the nozzle due to the skin effect, thereby creating an interface between the inner surface of the nozzle and the molten steel. A technique has been disclosed for heating the nozzle to prevent nozzle clogging.

However, in order to improve the quality of the slab by preventing segregation in the slab, it is necessary to maintain the molten steel at the lowest possible temperature during casting. Further, in order to prevent breakout during the casting process, the molten steel must be cast at as low a temperature as possible.

On the other hand, as already mentioned, the specific surface area of the molten metal passing through one injection nozzle continues to increase, and this, combined with the low-temperature casting, makes casting more likely to cause nozzle clogging.

Therefore, there is a need for a technology that can deal with both the cases where solidified metal adheres inside the nozzle and the discharge rate is reduced, or when the nozzle is clogged. The technology disclosed in Japanese Patent No. 130364 cannot be a sufficient condition for solving the technical problems of the present invention.H5 As described above, the conventional technology for preventing injection nozzle clogging has problems. was.

The purpose of this invention is to obtain a simple method for preventing clogging of an injection nozzle that solves the problems in the prior art described above. A voltage is applied between the molten metal within the nozzle or the nozzle to inject the molten metal into the mold.

A method for preventing clogging of a molten metal injection nozzle in continuous casting, characterized by heating one or both of the injection nozzles.

The present invention will be explained in detail below.

The present invention heats the molten metal injection nozzle or the inside of the molten metal in the tundish without using induction heating as in the prior art.

By applying a voltage between the molten metal in the mold, the molten metal in the nozzle for injecting the molten metal into the mold and either or both of the nozzles are directly energized and heated. This problem has been solved better, and FIG. 1 shows one aspect of the device configuration when implementing this invention.

In Figure 1, 1 is tanditsh, 2 is molten metal,
For example, molten steel. 3 and 7 are electrodes, and a voltage is applied between them. 4 is an injection nozzle;
Molten metal 2 is injected into the mold 5 from the dish. Its tip is immersed in the molten metal 6 inside the casting hood 5. 8 is the molten metal inside the injection nozzle 4. 9 is slab support roll% 1
0 is the solidified shell in the slab.

The electrode 7 is immersed in the molten metal 6 inside the mold 5.
When the electrode 3 is immersed in the molten metal 2 in the tundish 1 as a cathode and energized with the electrode 3 as the anode, the current flows from the electrode 3.
It flows into the electrode 7 via the injection nozzle 4 and the molten metal 8 in the injection nozzle.

In the case where the injection nozzle 4 is the part with the smallest cross-sectional area in the current flow path mentioned above.

The current density is maximum in this part. The amount of heat generated by the current (Joule heat) is proportional to the square of the current density, so the maximum amount of heat is generated at the nozzle, and the amount of heat generated by the nozzle is mainly due to the heat generated by the nozzle rather than the heating of the molten metal itself in the nozzle due to the voltage application. The method heats the molten metal that comes into contact with the nozzle to prevent the generation of solidified metal debris and prevent nozzle clogging.

When the nozzle cross-sectional area is not the minimum and the injection nozzle is completely filled with molten metal, the molten metal is heated mainly by the Joule heat generated inside the molten metal in the injection nozzle, and solidified metal is not produced. Even if solid metal is formed, the temperature rise in the solidified metal is significant, so it is easy to understand and will not be blocked.

Even if the injection nozzle 4 were to become clogged, creating a gap between this blockage and the molten metal section 6 in the mold, and interrupting the electric circuit caused by the bath molten metal, the injection nozzle 4 could be made of a material that functions as a circuit element. As a result, current flows from the molten metal 2 in the tundish 1 to the molten metal 6 in the mold 5 through the nozzle.

The injection nozzle 4 generates heat, heats and melts the solidified metal in the blockage from the surrounding area, and releases the blockage.

Therefore, in this case, the injection nozzle must not be an electrically perfect insulator, but must become a heating element when energized. For example, an injection nozzle made of alumina graphite may be used.

In this way, according to the method of the present invention, it is possible to prevent the injection nozzle 4 from being blocked in any case, or to restore the injection nozzle 4 from the blocked state to the flowing state.

Note that the electrodes 3 and 7 may be provided at any position as long as it has good conductivity with the molten metal. For example, instead of the cathode 7 in the embodiment shown in the figure, the copper plate of the mold 5 or the slab support roll 9 may be used as the cathode, and electricity may be applied through the solidified shell 10 of the slab.

In this case, in order to reduce the contact resistance, it is necessary to increase the contact area between the electrode and the slab.

With the configuration described above, the electrical resistance is maximized at the injection nozzle 40 portion, most of the supplied power is concentrated in the injection nozzle portion, and power consumption efficiency is also improved.

An embodiment of the method of the present invention will be briefly described.

Molten gold is cast at the lowest temperature possible, as described above. The level of the molten metal within the mold is continuously detected using, for example, a static capacitive displacement meter.
Even though the slab drawing speed does not change, the liquid level is 1'
, -f, and when it is detected that the voltage has fallen below a predetermined limit level, a voltage is automatically applied between the electrodes 3.7. Thereupon, the temperature of the molten metal in the injection nozzle 4 increases, the solidified metal is melted, and the discharge command is restored to the previous value.

When the injection nozzle 4 is blocked before the solidified metal is soaked, and the bottom drops from the blocked part to form a gap, and the molten metal no longer functions as a current-carrying element, the injection nozzle 4
For example, 20s! In the case of an injection nozzle of φ, a current of 130 KW at 3000 A is applied to raise the temperature by 30° C./bec.

By doing so, the injection nozzle can be restored from the blocked state to the flowing state.

The relationships between the temperature increase rate and '-force, and the temperature increase rate and current value at this time are shown in FIGS. 2 and 3 for each injection nozzle diameter level.

According to this invention, even in a continuous casting process of molten metal using an injection nozzle with a large specific surface area, it is possible to reliably prevent the injection nozzle from clogging or to restore it from a blocked state to a flowing state. This negates the great effect it has had on making continuous casting processes more diversified.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one aspect of an apparatus for implementing the present invention. Figure 2 is a diagram showing the relationship between power consumption and nozzle heating rate when heating the injection nozzle, and Figure 3 is a diagram showing the relationship between power consumption and nozzle temperature increase rate when heating the injection nozzle.
FIG. 3 is a diagram showing the relationship between the magnitude of input current when heating the injection nozzle and the rate of temperature increase of the nozzle. 3.7... Electrode, 4... Injection nozzle, 5... Mold. Agent: Patent attorney Masaaki Akizawa, 2 people, 1m Ben? 3 [￥] in the concave

Claims (1)

[Claims] (1) In the process of continuous casting of molten metal, a voltage is applied between the molten metal in the tundish and the molten metal in the mold, and the molten metal in the nozzle that injects all the molten metal into the mold or the injection nozzle collapses. A method for preventing clogging of a molten metal injection nozzle in continuous casting, characterized by heating one or both of them.