KR20080059992A - A scum removal at free surface of roll sump in twin roll strip casting process - Google Patents

Abstract

A method for removing scum on a surface of melt in a twin roll type continuous strip casting process is provided to finally increase actual yield of the slab by discharging scum on the surface of the melt at once at a proper time during casting, thereby preventing casting instability or slab edge quality deterioration caused by the generation of scum on the surface of the melt. A method for removing scum on a surface of melt in a twin roll type continuous strip casting process comprises: a melt surface observing step of checking scum on a surface of melt by a melt surface observing camera; a weir ascending step of ascending weirs(172) such that the weirs do not come in contact with molten steel if the melt surface is covered with scum; a melt surface level descending step of lowering an elevation of the melt surface to a minimum level(143) if the melt surface is covered with scum; a melt surface level ascending step of instantaneously ascending again the elevation of the melt surface to a maximum level(144) at a moment when a surface level of the melt reaches the minimum level; and a melt surface level maintaining step of maintaining the surface level of the melt to a target level(145) when the surface level of the melt has reached the maximum level, and the scum has been removed.

Description

A scum removal at free surface of roll sump in twin roll strip casting process}

1 is a schematic view showing a conventional twin roll continuous sheet casting device,

Figure 2 is a schematic diagram showing the hot water surface scum state during conventional twin roll continuous sheet casting,

Figure 3 is a schematic diagram showing the level of fluctuations in the level of the water surface scum removal method according to the present invention,

Figure 4 is a photograph showing a discharge scum scum discharge situation according to the present invention.

<Description of Symbols for Main Parts of Drawings>

10: casting roll 11: cooling water hole

12: brush roll 20: tundish

30: immersion nozzle 31: upper nozzle

32: lower nozzle 33: side discharge port

40: sump 41: molten steel

50: edge dam 60: cast

61: clot cell 70: meniscus shield

71: atmosphere gas supply nozzle 172: weir

143: minimum nipple level 144: highest nipple level

145: target level

The present invention relates to a method for removing the tang surface scum in a double-roll continuous sheet casting method, and more specifically, when excessive scum is formed during casting, the scum is easily lowered to the highest level and the scum is easily discharged and the scum is generated. The present invention relates to a method for removing the surface scum in a twin-roll continuous sheet casting method, which can prevent casting instability and degradation of cast steel edge quality, and finally increase cast error rate.

A schematic diagram of a twin roll continuous sheet casting apparatus is shown in FIG. 1. The molten steel 41 supplied to the sump 40 between the casting rolls 10 through the discharge hole 33 of the immersion nozzle 30 attached to the tundish 20 is the casting roll 10 and the edge dam 50. The molten steel is surrounded by the molten steel and the molten steel in contact with the casting roll 10 forms a solidification cell 61 on the surface of the casting roll 10 while losing heat in the direction of the center of the roll. Is rolled out of the roll by a pair of rolls rotating in opposite directions. On the upper surface of the molten steel, a meniscus shield 70 device is installed to block external air to prevent oxidation of the molten steel 41 by contact with the atmosphere, and the molten steel surface is provided through a gas supply nozzle 71 installed in the apparatus. By supplying an inert gas, the upper part of the bath surface is maintained in an inert atmosphere. In addition, since the amount of momentum of the molten steel 41 discharged from the immersion nozzle 30 is so large that it may cause turbulence, the weir 72 fixed to the meniscus shield 70 is installed for the purpose of controlling the flow of the molten steel 41. It is. While attempting to maintain the atmosphere on the surface of the bath as inert as possible during casting, it is difficult to secure 100% sealing and there is a possibility that oxides are partially formed on the surface. Weir 72 also serves as a kind of barrier (barrier) to prevent the oxide thus produced to reach the growing coagulation cell (61).

Among the molten steel supplied to the molten steel pool through the discharge port 33, many inclusions are contained, and since the inclusions have a smaller specific gravity than the molten steel, the molten steel floats to the molten steel pool surface at the moment of supply to the molten steel pool. The speed of rise increases nonlinearly with the size of the inclusions. Therefore, molten steel pool noodle is gradually covered with the oxidative inclusions generated from the noodle and floating inclusions as the casting surface, and in the worst case, the scum 42 is the main component of the molten pool as shown in FIG. Covered with. When the hot water surface is covered with scum 42, the scum existing between the casting roll 10 and the weir 72 does not escape between the weir and the weir due to the flow of molten steel, and is mixed into the solidification cell growing on the roll surface. Will cause. Overlapping scums are gradually lowered over time, causing them to fall off at any moment and enter the cast, causing roll damage or casting instability.

Therefore, if the hot surface is completely covered with scum, the scum should be discharged at a suitable time just before the next coiling to maintain the hot surface again, so that continuous casting is possible and a good cast is obtained. It becomes possible.

The present invention is to overcome the above-mentioned problems, the object of the present invention is that when the molten steel is supplied to the lower nozzle through the upper nozzle and exits the lower nozzle discharge port is supplied to the roll sump, remaining in the supplied molten steel Due to the difference in specific gravity with molten steel, the surface scum formed by the floating inclusions and the oxidative inclusions formed by reacting with oxygen from the surface of the casting is discharged at an appropriate time during casting to reduce casting instability and cast edge quality caused by the surface scum generation. This is to provide a method for removing the surface scum in the twin-roll continuous sheet casting method that can finally increase the error rate of the cast.

The present invention is to achieve the above object, in the double-roll continuous thin plate casting method in the method of removing the scum scum surface inspection step (200) to check the scum of the scum surface with the scum observation camera, and the molten steel is not touched when the scum surface is covered with scum To increase the weir 172 to raise the weir step (172), and if the floor is covered with scum, the level of the floor to lower the level of the floor to lower level (143) 400, and the level of the floor to the lowest level (143) When the level reaches the highest level 144 instantaneously rising to the highest level 144, and the level of the level when the level reaches the highest level and the scum is removed, the level of the level to maintain the level It is characterized in that the level maintenance step (600).

In addition, the lowest level 143 is characterized by being calculated as the lowest level ≤ (target level-lowest level) / target level x 100.

In addition, the lowest level 143 is characterized in that within the range of 0 to 22%.

In addition, the highest level 144 is characterized by being calculated as the highest level ≤ (highest level-target level) / target level x 100.

In addition, the highest level 144 is characterized in that within the range of 0 to 15%.

Hereinafter, with reference to the accompanying drawings will be described in more detail the configuration of the present invention.

Referring to Fig. 3, there is shown a schematic diagram of the level of fluctuations in the level of the water level scum removal method according to the present invention.

As shown, the immersion nozzle 130 is composed of a two-piece (top) of the upper nozzle 131 and the lower nozzle 132, the upper portion of the upper nozzle 131 is connected to the tundish and the lower portion of the lower nozzle It penetrates through the upper cover of 132 and is located at a predetermined position in the lower nozzle. The inside of the lower nozzle is completely sealed by the upper cover.

While casting is in progress, the hot water surface maintains the target level 145 to control the supply of molten steel 41 from the immersion nozzle 130 to maintain this level. When the floor is covered with scum, the operator checks this through the surface observation camera and raises the weir 172 so that the molten steel does not touch.

After raising the weir 172, the water level is primarily lowered to the lowest level 143. At this time, the lowest level 143 is a range in which the following conditions are satisfied, and the range is 0 to 22%.

Minimum level ≤ (target level-minimum level) / target level * 100

As soon as the water level reaches the lowest level 143, the level of the water level is raised secondarily to reach the highest level 144. The highest level 144 allows the following conditions to be satisfied and the range is 0 to 15%.

Highest level ≤ (highest level-target level) / target level * 100

At this time, the reason why the scum is discharged is that the rising force of the molten steel and the rotational force of the casting roll are combined with each other when the molten steel level is moved from the lowest level to the highest level. The scum is discharged to the roll surface at one time.

After the floor level reaches the highest level 144 after passing the lowest level 143, the level is finally maintained again at the target level when it is determined that the level of scum is sufficiently removed. While such a hot water level fluctuation is accompanied, the weir 172 should be raised enough so that the molten steel 41 does not touch. Therefore, the weir 172 should be taken to be sufficiently raised at the same time at the time when the water level is first to be the lowest level.

Hereinafter, the present invention will be described in more detail with reference to Examples.

<Example>

The thin plate was manufactured by the example of this invention using the twin-roll continuous thin plate casting apparatus.

-Common conditions for implementation

Target steel grade: stainless steel (STS304),

Casting speed: 50m / min

Sheet Size: Thickness 3.5mm × Width 1300mm,

Roll diameter: 1250mm,

Roll width: 1300mm,

Minimum Level: 10%

Highest Level: 7%

An application example according to the present invention is shown in FIG. 4. It can be seen that the surface scum is sharply reduced compared to the comparative example, and that the present invention has shown a very effective performance.

As described above, in the double-roll continuous sheet casting method according to the present invention, the scum removing method may bring about an improvement in the casting rate through cast stabilization and casting stabilization.

Claims (5)

A tangential observation step 200 of checking a scum of a tang surface with a tangential observation camera; Weir rising step 300 to raise the weir 172 so that the molten steel does not touch when the hot water is covered with scum; If the surface is covered with a scum, the surface level lowering step (400) for lowering the height of the surface to the lowest level (143); A rising level 500 in which the level of the rising surface instantaneously rises to the highest level 144 as soon as the rising surface level reaches the lowest level 143; Method of removing the scum in double-roll type continuous sheet casting method, characterized in that it comprises a surface level maintenance step (600) that maintains the surface level at the target level (145) when the scum level reaches to the highest level. The method of claim 1, The lowest level is a method of removing the scum surface scum in the twin roll continuous sheet casting method characterized in that it is calculated as follows. Minimum level ≤ (target level-minimum level) / target level * 100 The method of claim 2, The lowest level is a method of removing the scum surface scum in the double-roll continuous sheet casting method characterized in that in the range of 0 to 22%. The method of claim 1, The highest level is the scum removal method in the double-roll continuous sheet casting method characterized in that calculated as follows. Highest level ≤ (highest level-target level) / target level * 100 The method of claim 4, wherein The highest level is the scum removing method in the double-roll continuous sheet casting method characterized in that within the range of 0 to 15%.

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