KR20050065059A - Apparatus for improving qualtiy of edges of thin steel sheet strip in thin steel sheet continuous casting process - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the provision of an apparatus for improving the quality of a slab end part in a thin sheet casting process by continuous casting. The nozzle 10 (11) which supplies is provided, and supplies the gas to the center part of the roll 2 with the temperature and quantity of the atmospheric gas through the nozzle 10 which supplies a gas to the edge part of the said roll (2). Provided is an apparatus for improving the quality of the slab end part in a thin sheet casting process, characterized in that the supply of the atmosphere gas is made larger than the temperature and the amount of the atmosphere gas through the nozzle (11).

Description

APAPATUS FOR IMPROVING QUALTIY OF EDGES OF THIN STEEL SHEET STRIP IN THIN STEEL SHEET CONTINUOUS CASTING PROCESS}

The present invention relates to the provision of an apparatus for improving the quality of a slab end part in a thin sheet casting process by continuous casting.

In the sheet casting process by continuous casting, the portion of the compression end of the cast steel in the range of about 300 mm is delayed from solidification compared to the center portion. The reason why the solidification is delayed is that a large gas gap is generated between the cast and the roll, and the solidification is slow due to less heat transfer between the roll and the cast. For this reason, edge bulging may occur at the end of the cast steel. Particularly in the STS304 steel, a large amount of delta ferrite at the end of the slab remains in the final material, which causes magnetism to degrade the quality. For this reason, techniques have been proposed to prevent solidification at the end of cast pieces, but have not completely improved the problem of solidification at the end.

The oxide produced on the hot water surface in the sheet casting process is called a scum. Such scum is incorporated into the cast steel, which itself becomes a cast surface defect, and also causes the cast surface crack, which is a major problem of lowering the cast surface quality. In order to solve this problem, the hot water is filled with an inert gas to perform casting, but in this case, the generation of scum is greatly reduced, but the problem is not fundamentally solved. Thus, according to one prior art (PCT / JP02 / 03732), a scum dam 6 is provided as shown in Figs. 1 and 2, and a gas nozzle 7 between the scum dam 6 and the roll 2 is provided. Has been proposed to direct the flow of the molten steel 1 surface flow to the end of the roll 2 to prevent mixing of scum. However, in this method, if the flow rate of the gas injected from the gas nozzle 7 is large, the flow of molten steel surface flow is high, and the possibility of preventing scum from moving toward the roll increases, but the edge dam 5 and the roll 2 The molten steel solidifies at the tangent triplet, creating a skull. When such a skull is generated and mixed in the cast steel, not only the defect of the cast steel but also a flaw in the contact portion between the edge dam and the roll may cause molten steel to leak and the casting may be stopped. In addition, when the flow rate of the gas in the gas nozzle 7 is small, the flow of molten steel surface flow is weak, which increases the possibility of the scum moving toward the roll, so that the scum may be mixed in the cast steel. Therefore, there is a need for a method of preventing a scull from being generated while supplying a large amount of gas toward the end of the slab.

The present invention has been studied in this background, and its object is to promote solidification of the end of the slab during sheet casting by continuous casting to produce a good slab and to prevent the formation of a scull, which is a solid formed on the contact area of the edge dam and the roll It is to provide a device to.

In order to achieve the above object, the present invention promotes solidification of the end of the slab during sheet casting using a continuous casting mold to produce a good cast, and to prevent the formation of a skull, which is a solid formed in the area where the edge dam and the roll contacted Provided is an apparatus for supplying atmospheric gas to the end and center portions of the roll, respectively, with a higher amount of hotter gas to the end portion than the center portion.

To this end, the present invention separates and installs the gas nozzle 10 for supplying the atmosphere gas to the end of the roll 2 and the gas nozzle 11 for supplying the atmosphere gas to the center of the roll 2, as shown in FIG. (2) The amount of gas supplied through the nozzle 10 on the end side is increased by one or more times compared to the amount of gas supplied through the nozzle 11 on the center of the roll 2, and the end of the roll 2 The apparatus which supplies atmospheric gas on condition on which the temperature of the gas supplied from the nozzle 11 of the side increased 1 times or more with respect to the temperature of the gas supplied from the nozzle 10 of the center part is provided.

In order to promote solidification at the end of the slab during sheet casting, the gas gap 8 between the roll 2 and the slab should be minimized (see FIG. 3). Since the gas gap 8 occurs in the thermal expansion of the gas, it is necessary to minimize the thermal expansion of the gas.

When the roll 2 and the molten steel 1 contact each other, the gas on the surface of the roll rises due to the heat transfer from the molten steel and expands. Therefore, the thermal expansion amount corresponding to the temperature rise of gas becomes a gas gap. The temperature of the initial gas is the temperature of the feed gas, and the final gas temperature present in the dimple of the roll surface is generally the average of the surface temperature of the roll and the molten steel temperature. Therefore, the gas gap between the roll and the solidification shell is determined by the final gas temperature / temperature of the supplying gas.

To: temperature of feed gas

: Size of gas gap

As a result, if the temperature of the feed gas is increased, the size of the gas gap is reduced. In particular, the gas gap is reduced to 1/2 when the temperature of the gas to be supplied is heated to 300 degrees as compared with the case where the temperature of the gas to be supplied is the normal temperature.

q: Heat transfer amount from the solidification shell to the roll direction

: Size of Gas Gap

k: heat transfer coefficient of the gas

This reduction in gas gap has the effect of doubling the amount of heat transfer from the solidification shell to the roll direction. In the sheet casting process, since the solidification of the portion of the slab at most about 300 mm is delayed compared to the center portion, it is necessary to promote the end solidification. Therefore, when hot gas is supplied to the end of the roll and cold gas is supplied to the middle of the roll, the amount of heat transfer from the solidification shell to the roll direction is increased to promote solidification of the slab end.

When hot gas is supplied to the end of the roll 2, even if the gas supply amount is increased, the generation of skull is reduced at the triple point where the edge dam, the roll and the molten steel meet. In other words, when the same gas is supplied, less heat is extracted from the edge dam and the molten steel in the case of the hot gas, thereby reducing the generation of the skull.

In one embodiment of the present invention, a roll 2 of 1300 mm width was used, and a 3.4 mm slab was manufactured using nitrogen as the atmospheric gas. The surface of the roll 2 was Ni plated and a roughness of Ra 15 mu m was generated using shot blasting technique. And in order to prevent mixing of scum, the scum dam was provided in the part except the pole end of the roll 2. As shown in FIG. The amount of atmospheric gas supplied was 400 Nm ³ / hr in total. The feed amount was the same. In Example 2, the end gas supply amount and the central gas supply amount were 1.5 times different, but the gas supply temperature was the same. In the third embodiment, the gas supply amount at the end and the center is also differentiated, and the gas supply temperature at the end is increased to 400 degrees. When the conditions suggested by the present invention were used, not only the solidification of the slab end part was good, but there was also a small amount of scull formation, and the scum removal was very good.

<Table 1>

Example End Gas Supply Amount / Center Gas Supply Amount End gas supply temperature / center gas supply temperature Coagulation Skull generation Scum removal Remarks Example 1 One One x o △ Comparative material, uniform amount supply Example 2 1.5 One x x o Comparative material, room temperature gas supply Example 3 1.5 2.3 o o o The present invention

1 is a schematic diagram of a thin plate casting process,

Figure 2 is a schematic cross-sectional view showing a conventional atmosphere gas supply method in the thin sheet casting process,

Figure 3 is a schematic diagram of the generation of the gas gap when the molten steel and the roll is solidified in the thin sheet casting process,

Figure 4 is a schematic configuration diagram showing an atmosphere gas supply device proposed in the present invention.

Explanation of symbols on main parts of drawing

1: molten steel 2: roll 3: molten steel supply nozzle

4: meniscus shield 5: edge dam 6: scum dam

7 gas supply nozzle 8 roll surface roughness 9 solidification shell

10 end gas supply nozzle 11 center gas supply nozzle

Claims (1)

In sheet casting by continuous casting, nozzles 10 and 11 are respectively provided for supplying an atmosphere gas to an end portion and a center portion of a roll 2, and a nozzle 10 for supplying gas to an end portion of the roll 2 is provided. A thin plate, characterized in that for supplying the atmospheric gas by increasing the temperature and the amount of the atmospheric gas through a) than the temperature and the amount of the atmospheric gas through the nozzle 11 for supplying the gas to the center of the roll (2). Apparatus for improving the quality of cast end in the casting process.