JP2000084647A - Method for blowing gas into upper nozzle in tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of clogging of an immersion nozzle for continuous casting in a long time even in the case of using the ordinary refractory without using a specific refractory by specifying back pressure of gas blowing and blowing flow rate. SOLUTION: The gas is blown from the upper nozzle of a tundish. Then, the nozzle clogging is prevented by blowing the gas into molten metal flowing in the nozzle hole at the bottom part of the tundish. At this time, it is desirable to regulate the back pressure of the gas blowing to >=1.2 kg/m2G and the gas blowing flow rate to 5-10 Nl/min. This reason is because 1.2 kg/cm2G to the back pressure of gas blowing is necessary to uniformly blow in some degree. The upper limit is unnecessary to regulate but it is desirable to be <=7 kg/cm2C because of the raising cost of inert gas. The gas blowing flow rate may be <=10 Nl/min. However, in order to obtain the gas blowing effect, the flow rate is necessary to be >=5 Nl/min as the min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for blowing gas from a nozzle above a tundish for blowing gas into a molten metal flowing into a nozzle hole at the bottom of a tundish to prevent nozzle clogging.

[0002]

2. Description of the Related Art Normally, in continuous casting, molten steel in a ladle is received in a tundish, and the molten steel is cast from the tundish into a mold through a immersion nozzle. A sliding nozzle is used at the bottom of the tundish so that the nozzle opening can be adjusted.

In continuous casting using a submerged nozzle, if the operation is continued for a long time, alumina adheres to the inner wall of the nozzle, and the submerged nozzle tends to be clogged. When the nozzle is clogged, the molten steel flow discharged from the nozzle into the mold fluctuates, which causes a breakout or the like. In particular, when aluminum-killed steel is continuously cast, nozzle clogging occurs in a short time, which has a significant effect on slab quality. As described above, since the problem of the adhesion of alumina to the inner wall of the immersion nozzle has a significant effect on the quality of the cast slab, various preventive measures have been conventionally taken.

[0004] As one of the measures for preventing the adhesion of alumina, there is a method of blowing gas into the outflow molten steel using an upper nozzle. The upper nozzle of the tundish is buried in the refractory at the bottom of the tundish so as to surround the molten steel outlet of the nozzle hole, and is configured to blow an inert gas into the outflowing molten steel through porous bricks. That is, most of the alumina flowing out into the mold together with the molten steel by gas blowing floats on the molten metal surface in the mold without adhering to the inner wall of the immersion nozzle because the alumina is captured in the gas bubbles.

However, in the conventional nozzle on a tundish, since the porosity and the average pore diameter of the porous brick are large, there is a variation in the material of the brick, and argon gas is blown from the porous brick into the molten steel unevenly. That is, even if an attempt is made to supply gas uniformly to the entire brick, the gas is preferentially passed through a coarse portion (porous portion) of the brick and blown into the molten steel because the brick is coarse and dense. Therefore, gas is not blown into the molten steel from the high-density region of the brick, and alumina adheres to this region. When alumina grows by adhesion, nozzle clogging occurs in a short time. When the nozzle is clogged, the molten steel discharge flow becomes uneven, the level of the molten metal in the mold fluctuates, and operation troubles such as breakout occur.

As a countermeasure against the above problem, Japanese Patent Laid-Open No. 2-3076
No. 54 discloses a refractory in which gas-permeable pores of a refractory porous body of a nozzle on a tundish are formed with an average diameter of 25 μm or less.

[0007]

However, it is difficult to produce a homogeneous refractory having an average pore diameter of 25 microns or less as in the above-mentioned prior art, and there are few practical refractories.

The present invention solves the above-mentioned problems, and an object of the present invention is to prevent clogging of a submerged nozzle even when ordinary refractories are used and continuous casting is performed for a long time without special refractory construction. An object of the present invention is to provide a method for blowing gas from a nozzle on a tundish.

[0009]

The gist of the present invention is as follows. A method in which gas is blown into a molten metal flowing into a nozzle hole at the bottom of a tundish and gas is blown from a nozzle above the tundish which prevents nozzle clogging, wherein a back pressure of gas blowing is 1.2 kg / cm ² G or more, and gas is blown. A gas blowing method for a nozzle on a tundish, wherein a blowing flow rate is 5 to 10 Nl / min.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIG. 1 is a graph in which the horizontal axis and the vertical axis respectively represent the back pressure and the blowing flow rate when gas is blown from the nozzle above the tundish.

In the conventional blowing method, the back pressure is 0.5 to
1.0kg / cm ² G, blown gas flow rate is 10-30Nl / m
was in.

In this case, as shown in FIG. 2, since the back pressure is low, the gas flow rate becomes non-uniform due to a slight variation in the porosity of the upper nozzle brick, and the alumina adhesion of the immersion nozzle concentrates in a region where the gas flow rate is small. Then, it is considered that nozzle blockage occurs from that part.

On the other hand, when the blowing back pressure is increased as in the present application, the gas is blown more uniformly than in the past, and a sound immersion nozzle is secured for a long time even if the porosity slightly varies. be able to.

Next, the reasons for limiting the constituent elements of the present invention will be described. First, as for the back pressure for gas injection, a back pressure of 1.2 kg / cm ² G is required in order to blow the above-mentioned gas uniformly to some extent. Although there is no particular upper limit, 7 kg / cm ²
It is desirable to blow below G.

In the present invention, since the gas is blown uniformly, the flow rate of the gas to be blown is smaller than that of the conventional gas, and may be 10 Nl / min or less. However, in order to obtain the effect of gas injection, a flow rate of at least 5 Nl / min is required.

A method for securing the back pressure of the blown gas can be easily achieved by changing the thickness of the refractory through which the gas passes according to the porosity of the refractory.

[0017]

EXAMPLES The results of applying the present invention to actual continuous casting equipment will be described. FIG. 3 shows the nozzle on the tundish actually applied. In this embodiment, since the back pressure is high, the gas-injected refractory 1 is limited to a part of the upper nozzle 3 in order to suppress the leak, a brick having a porosity of 21.7% is used, and the surrounding area is used. Is surrounded by an iron plate 2 to prevent gas leakage.

Using such an upper nozzle, continuous casting was performed at a gas blowing back pressure of 2.0 kg / cm ² G and a gas flow rate of 10 Nl / min. Gas injection back pressure and gas flow rate are
The measurement was performed at a position about 3 m from the gas injection position in the middle of the gas supply pipe.

[0019] As a result, in all the tests using the actual machine 30 times, no immersion nozzle was found to have a clogging tendency within 5 hours in all the experiments.

[0020]

According to the present invention, since the gas blown into the upper nozzle is uniformly blown, the adhesion of alumina to the immersion nozzle does not occur, and the adhesion of alumina to the inner wall of the immersion nozzle can be effectively prevented. In addition, a special refractory for gas injection does not need to be used, and there is no concern that refractory costs increase.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram comparing a back pressure and a flow rate of a blown gas with a related art and the present invention.

FIG. 2 is an enlarged view of an upper nozzle and a diagram showing a state of a gas blowing flow rate.

FIG. 3 is a diagram showing an upper nozzle of the present invention used in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas injection refractory 2 Iron plate 3 Upper nozzle 4 Gas conduit 5 Gas pool room

Claims (1)

[Claims] 1. A method for blowing gas from a nozzle on a tundish for preventing gas from being clogged by blowing gas into a molten metal flowing into a nozzle hole at the bottom of a tundish, wherein the back pressure of gas blowing is 1.2 kg / cm ² G or more. And a gas blowing flow rate of 5 to 10 Nl / min.