JP2012218036A - Method and device for casting slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress inflow of air to near a gap between casting rolls, prevent a seal chamber from coming in contact with the casting rolls, and prevent excess and deficiency in the amount of inactive gas.SOLUTION: The device for casting a slab includes: a pair of the casting rolls 11a, 11b forming the roll gap G11; side weirs 12 in contact with axial end faces of both the casting rolls 11a, 11b; the seal chamber 13 in contact with both the side weirs 12 and covering the roll gap G11 and the casting rolls 11a, 11b from above; a molten steel supply means 15 capable of supplying molten steel 14 to between the casting rolls 11a, 11b from above; a gas supply pipe 18 for making the inactive gas 17 to flow into a space 16 surrounded by the seal chamber 13, the outer peripheral surfaces of the casting rolls 11a, 11b, and the side weirs 12 and having a control valve 23; a pressure detector 21 for detecting gas pressure in the seal chamber 13; and a calculation control device 22 for giving a valve opening/closing command V to the control valve 23 in response to a pressure detection signal P detected by the pressure detector 21.

Description

  The present invention relates to a slab casting method and a slab casting apparatus.

  Conventionally, in order to directly continuously cast a thin strip as a slab from molten steel, various twin roll type slab casting apparatuses have been proposed, and as such a slab casting apparatus, for example, There is a slab casting apparatus shown in the conventional example of Patent Document 1. The slab casting apparatus shown in the conventional example of Patent Document 1 includes a pair of left and right casting rolls arranged side by side, and a roll gap is formed between opposing surfaces of the casting roll. Inside each casting roll, cooling water can be circulated in order to suppress the temperature rise of the casting roll and promote solidification of the molten steel.

  Side weirs are provided on both end faces in the axial direction of the casting roll so as to contact the both end faces, and a molten steel reservoir is formed by the casting roll surface, the side weir, and the roll gap. And the molten steel which flowed down from the tundish arrange | positioned above a casting roll through a nozzle accumulates in a molten steel reservoir.

  Above the molten steel reservoir, a seal chamber is provided in which both ends in the casting roll axial direction abut against the inner surface of the side weir. The upper surface of the seal chamber is located below the upper end of the side dam, and the end side walls extending in the casting roll axial direction are integrated at both ends of the upper surface of the seal chamber in the radial direction of the casting roll and in the horizontal direction. The end side walls hang down and a slight gap is formed between the lower end and the outer peripheral surface of each casting roll.

  An inert gas can be continuously supplied into the space of the seal chamber through a gas supply pipe. The reason why the inert gas is supplied into the space of the seal chamber is to prevent oxidation of the molten steel liquid surface and surface cracking of the slab.

  In the slab casting apparatus shown in the conventional example of Patent Document 1, when continuously casting a strip as a slab, left and right castings are performed so that a roll gap corresponding to the thickness of the strip to be manufactured is formed. After setting the interval between the rotation centers of the rolls, the driving device is driven to rotate the opposed outer peripheral surfaces of the casting rolls so as to move from the upper side toward the roll gap.

  Next, when the molten steel supplied to the tundish flows down from the nozzle to the casting roll, the molten steel collects in the molten steel reservoir, and then is cooled by the rotating casting roll to form a solidified shell on the outer peripheral surface of the casting roll. Further, the strip is sent downward by the rotation of the casting roll.

  At this time, if the inert gas is continuously supplied from the gas supply pipe to the space inside the seal chamber, the space is maintained in an oxygen-free state, and oxidation of the molten steel between the casting rolls is suppressed. In addition, the inert gas supplied to the space of the seal chamber flows out of the seal chamber through a gap between the lower end of the end side wall and the outer peripheral surface of the casting roll.

JP 2002-113555 A

  However, in the slab casting apparatus shown in the conventional example of Patent Document 1, the amount of inert gas supplied to the space inside the seal chamber is increased, and the internal pressure of the space is increased to about 1,000 Pa as a gauge pressure. Even so, oxygen is present in the space at a concentration of about 0.2%. For this reason, manganese (Mn) contained in the molten steel is oxidized, and a coating layer of manganese oxide (MnO) is generated at a rate of 20 μm per 10 minutes on the outer peripheral surface of the casting roll.

  Also, carbon (C) contained in molten steel and refractory reacts with oxygen in the seal chamber space and decomposed oxygen of manganese oxide, and carbon monoxide (CO) bubbles are mixed into the molten steel between the casting rolls. However, this is a factor of surface cracking of the strip fed from the casting roll. Furthermore, when manufacturing a strip from aluminum killed steel, it is required to maintain the oxygen concentration in the space in the seal chamber at about 10 ppm in order to prevent oxidation of aluminum.

  Thus, even if the supply amount of the inert gas to the space inside the seal chamber is increased, the reason why oxygen exists in the space is about 50 accompanying the outer peripheral surface of the casting roll as the casting roll rotates. An air layer of ˜100 μm enters the space. The accompanying air layer accompanying the rotation of the casting roll is caused by the boundary layer effect and rough irregularities formed on the casting roll surface.

  In addition, when the gap between the lower end side wall provided at both ends of the casting chamber in the radial direction and in the horizontal direction of the seal chamber is narrow and the outer peripheral surface of the casting roll is narrow, the casting roll is caused by thermal deformation of the casting roll during casting. The lower end of the side wall of the seal chamber may come into contact with each other. If contact is made, the surface of the casting roll is damaged, and the scratch is transferred to the surface of the cast strip. As a result, the quality of the strip is deteriorated.

  Furthermore, when the gap between the lower end of the side wall of the seal chamber and the outer peripheral surface of the casting roll changes due to thermal deformation during casting, the oxygen concentration in the seal chamber increases if the flow rate of the inert gas blown is small. In addition, if the amount of the inert gas to be blown is increased more than necessary, the operating cost increases.

  In order to eliminate the problems of the conventional example, the present inventors have proposed a slab casting apparatus as shown in the embodiment of Patent Document 1. The basic configuration of the slab casting apparatus of the embodiment of Patent Document 1 is similar to the conventional slab casting apparatus of Patent Document 1, but the configuration of the seal chamber is different. That is, in the slab casting apparatus shown in the embodiment of Patent Document 1, the upper surface having a flat portion on both the outer side in the casting roll radial direction and in the horizontal direction of the seal chamber in the conventional slab casting apparatus of Patent Document 1; A seal chamber is formed by providing another space formed by an outer end side wall that hangs down from the outer end of the casting roll in the radial direction of the upper surface of the upper surface, and configures a horizontal direction in the casting roll radial direction of the seal chamber. At the lower end of the outer end side wall, a brush-like rotating body that extends in the casting roll axis direction and contacts the outer peripheral surface of the casting roll is provided.

  In the slab casting apparatus according to the embodiment of Patent Document 1, a strip is cast in the same manner as the conventional slab casting apparatus of Patent Document 1, but a brush-like rotation that rotates by the rotation of the slab casting roll. The air layer accompanying the casting roll is removed by the body, and the inert gas supplied to the space of the seal chamber flows into the space on the rotating body side from the gap, and outwards from between the strands of the brush-like rotating body Leaked.

  However, also in the slab casting apparatus shown in the embodiment of Patent Document 1, there is room for study to make the solution of the same problem as that of the conventional slab casting apparatus of Patent Document 1 more reliable. However, as a seal chamber, a larger space than the slab casting apparatus of the conventional example of Cited Document 1 and an additional mechanism such as a brush-like rotating body are required, which increases the size of the apparatus. Inviting, equipment costs and operation and maintenance costs become expensive.

The present invention has been made in view of the above circumstances, and even if the seal chamber is not enlarged, the inflow of air to the vicinity of the roll gap is suppressed, the seal chamber and the casting roll are not in contact with each other, and the inert gas It is an object of the present invention to provide a slab casting method and a slab casting apparatus that can improve the quality of a strip that has been cast in such a manner that no excess or deficiency occurs in the amount of the slab.
[Background to the Invention]

  As shown in FIG. 3, the inventors arrange a seal chamber 2 above a roll 1 that can be driven to rotate, and a gap extending in the axial direction of the roll 1 on the upstream end wall in the rotation direction of the roll 1. G1 (5 mm to 15 mm) is formed, and the downstream end wall in the rotation direction of the roll 1 has zero gap extending in the axial direction of the roll 1, and the sampling hole is formed in the downstream side wall. A test device having 3 was made. Then, nitrogen gas 4 was supplied from the upper part of the seal chamber 2, the gas in the seal chamber 2 was sampled from the sampling hole 3, and the sampled gas was analyzed by an oxygen analyzer to obtain the oxygen concentration. The rotation speed of the roll 1 was constant. Further, the pressure in the seal chamber 2 was appropriately determined.

An example of the relationship between the pressure (Pa) in the seal chamber 2 and the oxygen concentration (ppm) in this case is as shown in the graph of FIG. 4, and the flow rate (m ³ / min) of the nitrogen gas 4 and the oxygen concentration (ppm) An example of the relationship with () is as shown in the graph of FIG. Thus, in order to keep the oxygen concentration (ppm) from 10 ppm or more required for preventing oxidation of aluminum in molten steel to 100 ppm or less required for preventing oxidation of Mn or Si in molten steel. in the graph of FIG. 4, the pressure of the seal chamber 2 and 1Pa or more ~5Pa less, in the graph of FIG. 5, the minute that the flow rate of nitrogen gas 4 may be set to be ^{30 m} 3 / min or more ~80m ³ / min or less It was.

The method for casting the slab of claim 1 comprises:
Horizontally arranged to form a gap between the rolls and supply molten steel from a molten steel supply means between a pair of casting rolls having side weirs on both axial end faces, and solidify the molten steel by the casting roll, and cast the slab In this case, an inert gas is supplied to prevent the reaction between the molten steel and oxygen into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir installed at the upper part of the casting roll. In the piece casting method, the inert gas is supplied into the space so that the gas pressure in the space surrounded by the seal chamber, the outer peripheral surface of the casting roll, and the side dam becomes 1 Pa to 5 Pa.

The slab casting method of claim 2 comprises:
Horizontally arranged to form a gap between the rolls and supply molten steel from a molten steel supply means between a pair of casting rolls having side weirs on both axial end faces, and solidify the molten steel by the casting roll, and cast the slab In this case, an inert gas is supplied to prevent the reaction between the molten steel and oxygen into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir installed at the upper part of the casting roll. in single casting method, in which the flow rate of the inert gas supplied to the enclosed space by the seal chamber and the side weir and the outer peripheral surface of the casting roll than 30 m 3 / ^min or more ~80m 3 / ^min.

  The slab casting method of claim 3 is such that the gap between the casting roll and the seal chamber is 5 mm to 15 mm.

The slab casting apparatus according to claim 4 comprises:
A pair of casting rolls that are horizontally arranged to form a roll gap; side dams that are in contact with both axial end surfaces of both casting rolls; a seal chamber that is in contact with both side dams and covers the roll gap and the casting roll from above; Molten steel supply means capable of supplying molten steel between the casting rolls from above; a gas supply pipe having a control valve so as to allow an inert gas to flow into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir; A pressure detector for detecting a gas pressure in the seal chamber, and an arithmetic control device for giving a valve opening / closing command to the control valve in response to a pressure detection signal detected by the pressure detector. .

The slab casting apparatus according to claim 5 comprises:
A pair of casting rolls that are horizontally arranged to form a roll gap; side dams that are in contact with both axial end surfaces of both casting rolls; a seal chamber that is in contact with both side dams and covers the roll gap and the casting roll from above; Molten steel supply means capable of supplying molten steel between the casting rolls from above, and a control valve and a flow rate detector so as to allow the inert gas to flow into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir. A gas supply pipe and an arithmetic control device for giving a valve opening / closing command to the control valve in response to a flow rate detection signal detected by the flow rate detector are provided.

According to the slab casting method and slab casting apparatus according to claims 1 to 5 of the present invention, various excellent effects as described below can be obtained.
I) There is no excess or deficiency in the amount of inert gas in the seal chamber, and the inflow of air to the vicinity of the gap between the casting rolls is suppressed.
II) As a result, the oxygen concentration in the seal chamber is maintained at a desired value, the molten steel and oxygen do not react, the seal chamber and the casting roll do not come into contact, and the seal chamber and the casting during casting It is not affected by the change in the gap between the rolls.
III) Therefore, the quality of the cast strip can be improved.
IV) Since the gap between the casting roll and the seal chamber can be increased to some extent, the accuracy of the apparatus due to thermal deformation is relaxed, and the apparatus cost can be reduced.
V) The amount of inert gas used can be reduced, which is economical.
VI) Since the seal chamber does not increase in size, the equipment cost and the operation and maintenance cost can be reduced.

It is a side view which shows the outline | summary of an example of embodiment of the slab casting method and slab casting apparatus of this invention. It is a side view which shows the outline | summary of the other example of embodiment of the slab casting method and slab casting apparatus of this invention. It is a side view which shows the outline | summary of the relationship between a roll and a seal chamber when conducting the experiment which supplied the inert gas to the seal chamber and measured the oxygen concentration in a seal chamber. It is a graph which shows the relationship between the pressure in a seal chamber and oxygen concentration obtained by experiment by the apparatus of FIG. It is a graph which shows the relationship between the flow volume of nitrogen gas and oxygen concentration which were obtained by experiment by the apparatus of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of a conventional twin-roll type continuous casting machine. The continuous casting machine is adjacent so as to form a roll gap G11 and each outer peripheral surface can be rotated from the upper side toward the roll gap G11. A pair of casting rolls 11a and 11b pivotally supported by the pair, a pair of side weirs 12 in contact with both axial end surfaces of both casting rolls 11a and 11b, and a roll gap G11 and casting rolls 11a and 11b in contact with both side weirs 12. A seal chamber 13 that covers from above and a molten steel supply means 15 that can supply molten steel 14 from above to the casting rolls 11a and 11b are provided.

  Inside each of the casting rolls 11a and 11b, cooling water for suppressing the temperature rise of the casting rolls 11a and 11b and promoting the solidification of the molten steel 14 can flow.

  A gap G12 is formed between the seal chamber 13 and the outer peripheral surfaces of the casting rolls 11a and 11b so that the gap between the casting rolls 11a and 11b is narrow in order to avoid contact between them.

  Also connected to the seal chamber 13 is a gas supply pipe 18 for allowing an inert gas 17 such as nitrogen gas to flow into the outer periphery of the casting rolls 11a and 11b, the side weir 12 and the space 16 surrounded by the seal chamber 13. Has been.

  The molten steel supply means 15 is disposed above the seal chamber 13 and allows the molten steel 14 to be stored, and the molten steel 14 flows through the seal chamber 13 and between the tundish 19 and the casting rolls 11a and 11b. It is comprised with the nozzle 20 to be made.

  In FIG. 1, reference numeral 21 denotes a pressure detector for detecting the gas pressure in the seal chamber 13, and 22 denotes a pressure detection signal P from the pressure detector 21 to keep the inside of the seal chamber 13 at a predetermined pressure. An arithmetic control device 24 for obtaining a flow rate of an inert gas 17 such as nitrogen gas supplied to supply the control valve 23 connected to the gas supply pipe 18 and supplying a valve opening / closing command V; It is. In the arithmetic and control unit 22, function generating means and a map are set.

Next, the operation of the illustrated example will be described.
When the band plate 25 is manufactured by the twin roll type continuous casting machine shown in FIG. 1, each of the casting rolls 11a and 11b is formed so that a roll gap Gl1 corresponding to the thickness of the band plate 25 to be manufactured is formed. After setting the interval between the rotation centers, the casting rolls 11a and 11b are rotated so that the opposing outer peripheral surfaces move from the upper side toward the roll gap Gl1.

  Next, when the molten steel 14 is supplied to the tundish 19 and the molten steel 14 is caused to flow down from the nozzle 20 to the casting rolls 11a and 11b, a solidified shell 25 'is formed on the outer peripheral surfaces of the casting rolls 11a and 11b. The band plate 25 is sent downward by the rotation of the rolls 11a and 11b.

At this time, the inert gas 17 is continuously supplied from the gas supply pipe 18 to the space 16 inside the seal chamber 13, and the gap G12 between the seal chamber 13 and the outer peripheral surfaces of the casting rolls 11a and 11b is outwardly provided. By flowing out, the air is prevented from flowing in from the gap G12, the space 16 is made oxygen-free, and the oxidation of the molten steel 14 between the casting rolls 11a and 11b is suppressed.

  Thus, the pressure of the gas in the seal chamber 2 detected by the pressure detector 21 is given to the arithmetic control device 22 as the pressure detection signal P, and the arithmetic control device 22 passes the gas supply pipe 18 into the seal chamber 13. The flow rate of the supplied inert gas 17 is obtained, and a valve opening / closing command V corresponding to the obtained flow rate of the inert gas 17 is given to the control valve 23. Therefore, the opening degree of the control valve 23 is adjusted to a predetermined opening degree, and the inert gas 17 from the inert gas production device 24 is supplied into the space 16 of the seal chamber 13 through the gas supply pipe 18.

  According to the illustrated example, the amount of the inert gas 17 in the seal chamber 13 is not excessive or insufficient, and the inflow of air to the vicinity of the gap between the casting rolls 11a and 11b is suppressed. As a result, the oxygen concentration in the seal chamber 13 is maintained at a desired value, the molten steel 14 and oxygen do not react, the seal chamber 13 and the casting rolls 11a and 11b do not come into contact with each other, and casting is in progress. It is not affected by the change of the gap G12. Accordingly, the quality of the cast strip 25 can be improved.

  Further, since the gap G12 can be increased to some extent, the accuracy of the apparatus due to thermal deformation can be relaxed, the apparatus cost can be reduced, and the amount of the inert gas 17 used can be reduced. Furthermore, since it is not necessary to make the seal chamber 13 so large, the equipment cost and the operation and maintenance cost can be reduced.

  FIG. 2 shows another example of the embodiment of the present invention. In the illustrated example, the flow rate of the inert gas 17 flowing through the gas supply pipe 18 is not based on the gas pressure in the seal chamber 13, The flow rate of the inert gas 17 supplied into the seal chamber 13 is controlled.

  In the figure, reference numeral 26 denotes a flow rate detector connected to the gas supply pipe 18 so as to be located downstream of the control valve 23 in the flow direction of the inert gas, and the flow rate detection signal F of the inert gas 17 detected by the flow rate detector 26. Can be given to the arithmetic and control unit 22. Further, when the flow rate detection signal F of the inert gas 17 is deviated from a predetermined flow rate range, the arithmetic control unit 22 obtains the opening degree of the control valve 23 from the deviation amount, and a valve opening / closing command corresponding to the opening degree. V can be supplied to the control valve 23.

  The strip 25 is cast in the same manner as in FIG. At this time, the flow rate of the inert gas 17 detected by the flow rate detector 26 is given to the arithmetic and control unit 22 as a flow rate detection signal F, and the opening degree of the control valve 23 is obtained in the arithmetic and control unit 22, and the obtained opening degree is obtained. The degree is given to the control valve 23 as a valve opening / closing command V, and the opening degree of the control valve 23 is adjusted to a predetermined state.

Also in the illustrated example, the amount of the inert gas 17 in the inner space 16 of the seal chamber 13 is not excessive or insufficient, and the inflow of air to the vicinity of the gap between the casting rolls 11a and 11b is suppressed. Similar effects can be obtained.

  In addition, according to the example of illustration of this invention, although the case where nitrogen gas was used as an inert gas was demonstrated, it does not deviate from the summary of this invention that an inert gas is not limited to nitrogen gas. Of course, various changes can be made within the range.

11a, 1b Cast hole 12 Side weir 13 Seal chamber 14 Molten steel 15 Molten steel supply means 16 Space 17 Inert gas 18 Gas supply pipe 25 Strip (slab)
21 Pressure detector 22 Arithmetic controller 23 Control valve 26 Flow rate detector G1l Roll gap G12 Gap P Pressure detection signal F Flow rate detection signal

Claims (5)

  Horizontally arranged to form a gap between the rolls and supply molten steel from a molten steel supply means between a pair of casting rolls having side weirs on both axial end faces, and solidify the molten steel by the casting roll, and cast the slab In this case, an inert gas is supplied to prevent the reaction between the molten steel and oxygen into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir installed at the upper part of the casting roll. In the piece casting method, an inert gas is supplied into the space so that the gas pressure in the space surrounded by the seal chamber, the outer peripheral surface of the casting roll, and the side weir is 1 Pa to 5 Pa. Slab casting method. Horizontally arranged to form a gap between the rolls and supply molten steel from a molten steel supply means between a pair of casting rolls having side weirs on both axial end faces, and solidify the molten steel by the casting roll, and cast the slab In this case, an inert gas is supplied to prevent the reaction between the molten steel and oxygen into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir installed at the upper part of the casting roll. in single casting method, characterized in that the flow rate of the inert gas supplied to the seal chamber and the side weirs and the space surrounded by the outer peripheral surface of the casting roll than 30 m 3 / ^min or more ~80m 3 / ^min Slab casting method.   The slab casting method according to claim 1 or 2, wherein a gap between the casting roll and the seal chamber is 5 mm to 15 mm.   A pair of casting rolls that are horizontally arranged to form a roll gap; side dams that are in contact with both axial end surfaces of both casting rolls; a seal chamber that is in contact with both side dams and covers the roll gap and the casting roll from above; Molten steel supply means capable of supplying molten steel between the casting rolls from above; a gas supply pipe having a control valve so as to allow an inert gas to flow into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir; A pressure output device for detecting a gas pressure in the seal chamber, and an arithmetic control device for giving a valve opening / closing command to the control valve in response to a pressure detection signal detected by the pressure detector. A slab casting device.   A pair of casting rolls that are horizontally arranged to form a roll gap; a side weir that is in contact with the axial end surfaces of both casting rolls; a seal chamber that is in contact with both side weirs and covers the roll gap and the casting roll from above; A molten steel supply means capable of supplying molten steel between the casting rolls, and a gas having a control valve and a flow rate detector so that the inert gas flows into the space surrounded by the seal chamber and the outer peripheral surface of the casting roll and the side weir. A slab casting apparatus comprising: a supply pipe; and an arithmetic control unit that gives a valve opening / closing command to the control valve in response to a flow rate detection signal detected by the flow rate detector.

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