JPH0732104A - Method for supplying powder for continuous casting - Google Patents

Abstract

PURPOSE:To drastically improve the surface quality of a cast slab by smoothly supplying powder into a mold. CONSTITUTION:In a method for heating and supplying the powder into the mold 1 for continuous casting, the powder is heated to the temp. developing the fluidity without changing the constituting components and material property value by using hot blast 7 in a vessel 6 on the way of supplying the powder and supplied into the mold by gas stream carrying 8. By this method, the temp. drop near a meniscus is prevented and the surface defect, such as pin hole, entrapment of slag, can drastically be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating and supplying powder into a mold in continuous casting.

[0002]

2. Description of the Related Art In continuous casting, in which molten steel is poured into a mold and continuously cast by pulling out a slab with a roll while cooling in the primary cooling and secondary cooling zones in the mold, Immersion nozzle to inject molten steel below,
A powder supply device for coating the molten steel surface in the mold and an oscillation device for vertically moving the mold are used. The powder plays a role of preventing oxidation of the surface of the molten steel in the mold, lubricating between the mold and the slab, capturing floating inclusions, and keeping the surface of the molten steel in the mold warm.

The powder supply into the mold in the above continuous casting has conventionally been a spraying method by mechanical transportation using a spring feeder or the like, but there is a problem that the reliability of the apparatus is low due to thermal problems. An air flow transportation method has also been tried, but there are problems in that the working environment is deteriorated due to dust generation and the transportation cost is low. Furthermore, the powder is normally supplied into the mold at room temperature, inevitably cooling the meniscus at the top end of the molten steel surface, biting the slag by skinning of the molten steel surface, the surface of slabs such as pinholes. It is known to cause defects.

As a method of preventing such a temperature drop in the meniscus portion, there are powdering (usually granules) and use of heat-generating powder. The exothermic powder is a metal powder such as Ca-Al or Ca-Si added as a constituent component, which is oxidized in the mold to keep the meniscus portion warm by the heat generated at this time. However, the powder powder does not have sufficient heat retention effect, and
The heat-generating powder causes a rapid reaction of the heat-generating agent, does not maintain the heat-generating effect, does not provide a continuous heat-retaining effect, and is not expected to dramatically improve the surface quality of the slab. The exothermic powder also deteriorates the internal quality of the cast slab by using Fe ₂ O ₃ contained as an oxidation source and oxides such as Al ₂ O ₃ and SiO ₂ which are oxidation reaction products as inclusions.

As a method for solving the above problems, the powder is heated to a temperature at which the constituent components and physical properties of the powder do not change during the powder supply process, and the heated powder is put into a mold (Japanese Patent Laid-Open No. 1443052). Gazette), the powder is heated in the container during the powder supply process using microwaves, and the heating temperature is set to a temperature at which the constituent components and physical properties of the powder do not change, and the heated powder is charged into the mold. (JP-A-4-14
No. 3053) is proposed.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Patent Application No. 052 and Japanese Patent Application Laid-Open No. 4-143053 is heated to a temperature at which the constituent components and physical properties of the powder do not change during the powder supply process and charged into the mold. A screw-type continuous cutting device is used for charging into the inside, which corresponds to the spraying method by mechanical transportation, and there are problems such as low reliability of the device due to thermal problems.

The object of the present invention is to eliminate the drawbacks of the method of supplying the heated powder into the mold and to smoothly supply the powder into the mold without deteriorating the working environment due to dust generation. It is an object of the present invention to provide a method for supplying powder for continuous casting which can significantly improve the surface quality of one surface.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted various tests and examinations in order to achieve the above object. As a result, it was confirmed that if the fluidity is improved by heating the powder, a small amount of gas can be carried by air flow, and the deterioration of the working environment due to the generation of dust due to air flow transport can be prevented, and the present invention has been reached.

That is, according to the present invention, in a method of heating and supplying powder into a continuous casting mold, the constituent components and physical properties of the powder are not changed by using hot air in the container during the powder supply process, and A method for supplying powder for continuous casting, which comprises heating to a temperature at which fluidity is generated and supplying the powder into the mold by air flow transportation.

[0010]

In the present invention, the constituent components and physical properties of the powder are not changed by using hot air in the container during the powder supply process, and the powder is heated to a temperature at which fluidity of the powder is generated, and the powder is transported by air flow to the mold. Since it is supplied inside, compared with the case of air-powdered powder at room temperature,
With the same amount of transportation, the amount of transportation gas can be reduced to 1/3 or less, and the deterioration of the work environment and the increase of transportation cost due to dust generation accompanying airflow transportation can be suppressed. Further, it is possible to suppress the temperature decrease of the meniscus portion by the powder heating and the air flow transportation by hot air, and it is possible to suppress the deterioration of the surface quality of the slab due to the biting of the slag, the pinhole and the like.

The heating temperature of the powder in the present invention is
The temperature at which the flowability of the powder occurs, for example, 100 to 30 without changing the constituent components and physical properties of the powder.
It is desirable to heat using an inert gas having a high temperature of about 0 ° C. However, since the fluidity of the powder changes depending on the heating temperature and the amount of carbon added to the powder, the fluidity of the powder can be controlled by the heating temperature and the amount of carbon added to the powder, and a small amount of dry hot gas can be used for air flow transport. It is important to give a certain degree of fluidity. As the gas used for air flow transportation of the powder in the present invention, nitrogen gas, inert gas such as argon gas, air and the like are considered, but it is possible to prevent deterioration of the powder by using the same heated nitrogen gas as the hot air for heating the powder. And it is preferable from the viewpoint of cost.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to FIGS. FIG. 1 is a side sectional view showing an example of an apparatus for carrying out the method of the present invention, FIG. 2 is a graph showing the relationship between the heating temperature of powder and the fluidity index, and FIG. 3 is the carbon content added to the powder and the fluidity index. 4 is a graph showing the relationship between the flow rate of the transferred gas and the amount of powder cut out at room temperature and 200 ° C. heating, and FIG. 5 is the distance from the meniscus at room temperature and 200 to 300 ° C. heating. FIG. 6 is a graph showing the relationship between the heating temperature of powder and the index of oscillating nail depth, and FIG. 7 is a graph showing the relationship between the heating temperature of powder and the index of surface flaw generation. .

In FIG. 1, 1 is a casting mold for continuous casting, and 2 is a casting mold.
Is a tundish immersion nozzle (not shown) for injecting molten steel below the upper surface of the molten steel 3 in the mold 1, 4 is a solidified shell which is cooled by the mold 1 and is generated on the surface of the slab, 5 is the upper surface of the molten steel 3 in the mold 1. Powder, 6 is a powder hopper, 7 is a hot air blowing tube provided at the bottom of the hopper 6,
The powder in the hopper 6 is heated to a temperature at which the powder constituents and physical properties do not change and fluidity of the powder occurs, for example, 100 to 300 ° C. in this case,
As shown in Fig. 2 and Fig. 3, the fluidity of the powder changes depending on the heating temperature and the amount of carbon added to the powder. Therefore, the fluidity of the powder is controlled by the heating temperature and the amount of carbon added to the powder, and a small amount of drying is performed. It imparts fluidity to the extent that it can be transported by air by the gas.
Reference numeral 8 denotes a transfer gas blowing section for air-transporting the powder from the lower part of the hopper 6 into the mold 1 through the powder supply pipe 9, and is configured to supply the powder into the mold 1 at a predetermined supply speed.

With the above-described structure, the powder has a temperature at which the constituent components and physical properties of the powder are not changed by the hot air blown from the lower hot air blowing pipe 7 in the hopper 6, and the fluidity of the powder is generated.
For example, it is heated to 200 ° C. to impart fluidity. The powder heated to 200 ° C. in the hopper 6 and imparted with fluidity is air-transported in the powder supply pipe 9 by a transfer gas, for example, nitrogen gas, which is blown from the transfer gas blowing portion 8 in the lower part of the hopper 6, and a predetermined supply is performed. It is fed into the mold 1 at a speed. In this case, since the powder is heated and has fluidity, as shown in FIG. 4, as compared with the case where the powder at room temperature is transported by air, if the amount of gas to be transferred is three times or more, Can be supplied, and the generation of dust and the transportation cost can be reduced by reducing the amount of gas to be transferred and improving the fluidity.

The powder supplied into the mold 1 is
Since it is heated to 200 ° C., as shown in FIG. 5, the temperature drop in the vicinity of the meniscus is small as compared with the case where the powder is supplied into the mold 1 at room temperature. By reducing the temperature drop in the vicinity of the meniscus, as shown in FIG.
As shown in, the nail depth of the oscillation becomes smaller. This means that the bubbles and inclusions trapped by the nail of the oscillation are reduced. further,
In terms of the surface quality of the slab, as shown in FIG. 7, by heating the powder, the surface flaw generation ratio can be significantly reduced.

[0016]

As described above, according to the method of the present invention, when the powder is heated and fed into the continuous casting mold, the powder is fluidized so that the powder can be pneumatically transported by a small amount of the transfer gas. The powder can be smoothly supplied into the mold without generating dust or transfer cost. Further, the temperature of the vicinity of the meniscus is prevented from being lowered by heating the powder, and the slab surface defects due to pinholes, slag entrapment, etc. can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an example of an apparatus for carrying out the method of the present invention.

FIG. 2 is a graph showing the relationship between the heating temperature of powder and the fluidity index.

FIG. 3 is a graph showing the relationship between the ratio of carbon added to powder and the fluidity index.

FIG. 4 is a graph showing the relationship between the flow rate of transferred gas and the amount of powder cut out when heated at room temperature and 200 ° C.

FIG. 5 is a graph showing the difference between the solidification temperature and the distance from the meniscus when heated at room temperature and 200 to 300 ° C.

FIG. 6 is a graph showing a relationship between a powder heating temperature and an oscillation nail depth index.

FIG. 7 is a graph showing the relationship between the powder heating temperature and the surface flaw generation index.

[Explanation of symbols]

 1 Mold 2 Immersion Nozzle 3 Molten Steel 4 Solidification Shell 5 Powder 6 Hopper 7 Hot Air Blowing Pipe 8 Transfer Gas Blowing Port 9 Powder Supply Pipe

Claims (2)

[Claims] 1. A method for heating and supplying powder into a continuous casting mold, wherein hot powder is used in the container during the powder supply process without changing the constituent components and physical properties of the powder, and the fluidity of the powder is improved. A method for supplying powder for continuous casting, which comprises heating to a temperature at which it is generated and supplying the powder into the mold by air flow. 2. The method of supplying powder for continuous casting according to claim 1, wherein the powder is transported by hot air.