JP3508339B2 - Casting termination method in continuous casting - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of ending casting in continuous casting, and more particularly to a method of extracting the top of a slab from a mold without leaking steel from the top of the slab. The present invention relates to a method for terminating continuous casting that can be performed. [0002] In the case of ending the casting in continuous casting, when the residual molten steel in the tundish reaches a predetermined amount, the casting speed is reduced and hot water supply from the immersion nozzle into the mold is stopped. Generally, a method of putting a coolant into the molten steel in the inside or applying cooling water to solidify a top portion and then pulling out a slab is generally used. However, as shown in JP-A-6-226414 and JP-A-6-262323, such a method has the following problems. (1) Since the casting speed is greatly reduced or stopped before the end of casting, productivity decreases. (2) Slab bulging occurs between the supporting rolls due to a large reduction or stoppage of the casting speed, resulting in a slab defect. (3) Even if the coolant is supplied, unsolidified molten steel is squeezed out from the top part by pulling out by slab bulging, leaking steel is seen, and base metal adheres to support rolls, etc., and the next casting It is an obstacle. (4) It takes time and effort to supply coolant. Further, in the case of the late solidification light reduction method which has been actively developed in recent years, or when a thin cast piece is manufactured by actively crushing an unsolidified portion of a cast cast piece, the casting is also performed at the end of casting. If the reduction is continued as it is, the unsolidified molten steel equivalent to the length from the reduction position to the mold is squeezed out to the mold side by the drawing at the end, and the leaked steel occurs between the mold and the support roll, as described above. As in the case of the above, the next casting is disturbed. JP-A-6-226414 and JP-A-6-226414
The method proposed in Japanese Patent No. 262323 is a method for terminating casting without reduction, but there are the following problems when applying these methods. For example, when the method disclosed in Japanese Patent Application Laid-Open No. 6-226424 is used, (1) the productivity is decreased because the casting speed at the end of casting must be 0.2 m / min or less. (2) In the case of light reduction, the solidification completed area is moved to the mold side by lowering the casting speed, so that the intended purpose is not achieved. Must be strong. The method disclosed in Japanese Patent Application Laid-Open No. 6-262323 is a method in which the top of the slab is solidified with secondary cooling water.
When a cast slab is drawn with a reduction, unsolidified molten steel is squeezed out. There is a problem in equipment. [0009] Therefore, as a method of lightly reducing the pressure of the unsolidified portion, for example, JP-A-6-7909 and JP-A-60-60
A method disclosed in -250864 has been proposed. According to this, a metal frame for accommodating unsolidified molten steel discharged by rolling is mounted to prevent steel leakage from the top of the slab. However, as described above, these methods are as follows: (1) Preparing for the preparation of the metal frame (2) Time and effort for mounting the metal frame into the mold quickly and quickly at the end of casting (3) The cross section of the mold is The larger the size, the larger the metal frame, and the more difficult it is to mount. (4) Since the tundish must be raised at the same time as casting and moved, the metal frame cannot be mounted (because the immersion nozzle is an obstacle), It takes 30 to 60 seconds, and thus has the disadvantage that the casting speed must be extremely reduced. [0011] The object of the present invention is to solve the problem of molten steel leaked steel which was inevitable in the active reduction method (large reduction method) of the solidified portion of the slab including the light reduction method. An object of the present invention is to provide a method for terminating a casting in which the top of a slab can be pulled out while effectively avoiding the need for mounting a metal frame or the like. Means for Solving the Problems Accordingly, the present inventors have
In order to achieve such an object, various studies are repeated, and rather, a solidified shell is positively formed along the mold wall in the mold, so that the slab, especially when the slab is finally extracted from the mold, is removed from the slab. The present inventors have found that leaked steel can be effectively prevented, and have completed the present invention. Therefore, the present invention is a method for terminating casting while continuously drawing a slab obtained while solidifying molten steel in a mold, and completing the supply of molten steel from the tundish into the mold. In doing so, first lower the casting speed, then by forcibly crushing the slab in the thickness direction with a reduction segment disposed directly below or below the mold,
Molten steel slab is at overflowing toward the outermost top upward by Rukoto into contact with the mold walls, while the slab is within the mold, the inner
By generating a solidified wall having unsolidified molten steel in the portion , and by returning the rolling-down segment that crushed the slab before the slab that generated the solidified wall at the top of the slab falls out of the mold. By bulging the slab in contact with the reduction segment, the inside of the solidified wall is
Reduce the level of molten steel to at least the inside of the solidification wall
This is a method of terminating casting in continuous casting, which comprises forming a space and allows the top of the slab to be pulled out of the mold without leakage of steel from the top of the slab. Next, the operation of the present invention will be described more specifically with reference to the accompanying drawings. FIG.
It is a block diagram of the continuous casting equipment for unsolidified rolling which can complete | finish casting by the method concerning this invention, FIG. 2: is explanatory drawing which shows the rolling state before completion | finish of casting, and FIG. 3 opened the rolling segment. FIG. 9 is an explanatory diagram showing a state at the time. The present invention will be described with reference to FIGS. 1 to 3. In the case where the continuous casting method is to be ended while reducing the unsolidified portion of the slab including the slab in the final stage of solidification, first, as shown in FIG. From the state of the steady casting speed (Vc), it is detected by the load cell 23 that measures the weight of the molten steel 4 that the molten steel 4 in the tundish 1 has reached a predetermined residual steel amount. Then, a command is sent from the host controller to the casting speed controller to reduce the casting speed.
At this time, the casting speed is, for example, from a steady speed of 3 to 5 m / min to 1
Decelerate to ~ 2m / min. Conventionally, the deceleration at this time was almost stopped at 0 to 0.5 m / min. Thus, before the molten steel is supplied into the mold 1, the completely solidified position (crater end portion) is moved from the pressing guide roll region (13-1 to 13-5) to the mold side. At the same time, the reduction zone in the reduction guide roll region can be moved to the mold side. In addition,
The position of the crater end changes according to the casting speed according to the following equation. [Equation 1] In order to improve center segregation and porosity by lowering the crater end portion of the slab even in the method of casting a slab by unsolidification reduction, it is necessary to reduce the vicinity of the crater end portion as well. It is necessary to change the casting speed depending on the type of steel and the degree of superheat of the molten steel. For this purpose, a plurality of rolling-down segments are generally provided in the rolling-down zone 13 as shown in FIG. Next, a description will be given of the pressure control of the hydraulic pressure reduction cylinder of the pressure reduction guide roll (reduction segment) when the casting is completed from the time of casting at the steady casting speed Vc. In FIG. 1, when the casting is performed at a steady casting speed (Vc), the rolling-down segments 13 (13-1 to 13-1) are used.
13-5) The hydraulic pressure P (kg / cm ² ) applied to the reduction cylinder 14 can be approximately expressed by the following equation. [Equation 2] As can be seen from the equation (1), since the crater end portion approaches the mold side by lowering the casting speed, the reduction amount (D-Dt) of the solidified slab 17 by the reduction segment on the mold side increases. The hydraulic pressure corresponding to the increase in the reduction reaction force on the short side surface shown by the equation (2) is increased via the hydraulic controller. On the other hand, the pressure applied from the crater end to the hydraulic cylinder of the later rolling down segment is
By lowering (reducing) the pressure equivalent to the hydraulic pressure corresponding to the reduction reaction force on the short side surface shown in equation (2) from the pressure before lowering Vc, the reduction of the crater end is maintained, and An object of the present invention is to prevent slab bulging in a reduction segment. By applying a hydraulic pressure equivalent to the static iron force + the rolling reaction force to each of the rolling segments to the respective cylinders, the slab is reduced, and the rolling segments subsequent to the rolling segment are applied to the respective rolling segments. The slab reduced in the reduction segment by applying a hydraulic pressure equivalent to the static iron force + α equivalent to the applied molten steel static pressure to the hydraulic cylinder is the thickness along the reduction gradient (reduction amount / roll pitch of the reduction segment × number of rolls). It becomes a slab with a direction taper,
The rolling segment arranged after the rolling segment cannot be reduced by the hydraulic pressure of the amount corresponding to the static iron pressure + α, and therefore floats. In the drawing, reference numeral 27 denotes a foot roll at the lower part of the mold, 19 to 22 denote pinch rolls, 20 denotes a lower roll fixing frame, 15 denotes a fixed frame of a pressing segment, and 16 denotes a movable frame. FIG. 2 shows a rolling state when the casting speed is reduced in this way. The rolling-down segments 13-1 to 13-5 may be segments including any of a single roll or a plurality of rolls. When the casting speed is reduced to a predetermined casting speed Vi before the end of the casting, the length Li to the crater end portion is expressed by the following equation. [Equation 3] Next, the molten steel 4 from the tundish 1 is supplied to the mold by closing the nozzle 2 by closing the nozzle 2. At this time, a rolling zone immediately below the mold is formed until the unsolidified slab 5 does not come out of the mold. When the unsolidified slab 5 is reduced in step 13, as shown in FIG. 2, unsolidified molten steel overflows from the top of the slab in the mold 3, and the unsolidified molten steel comes into contact with the mold wall to form the solidified shell 26. Will make it. That is, after reaching this state, the mold 3
When the hot water supply to the mold is stopped, the molten metal surface 24 is drawn out at a low casting speed, so that the unsolidified molten steel 5 is discharged from the top of the slab into the mold by the reduction of the reduction segment 13-1, and contacts the mold wall. The solidified shell 26 is drawn out. There is no particular problem if the hot water supply is stopped before, at the same time as, or after the reduction of the reduction segment 13-1. In the present invention, including these cases, it is referred to as "ending hot water supply". Next, as shown in FIG. 3, when the squeezing segment 13-1 is opened while the slab exists under the mold, the molten steel discharged into the mold is sucked to form a space 25 surrounded by the solidified shell 26. By creating this space, overflow from the top of the slab can be prevented, and at the same time, the reduction segments 13-2, 13-3, ... are equivalent to tension output by static iron pressure corresponding to the unsolidified length Lf. By adjusting the pressure of the hydraulic cylinders 14 of the respective pressure-reducing segments so as to have a slight positive force, the cast slab can be pulled out as it is, and steel leakage can be prevented. When the reduction amount is small, the reduction segment 13-1
In addition, the space 25 can be secured by opening 13-2 and further 13-3. It is necessary to consider the heat shrinkage of the solidified shell between the space 25 and the amount of reduction, but it is sufficient that the relationship expressed by the following expression be established approximately, ignoring it. [Equation 4] The situation at this time is shown in FIG.
After that, the rolling segments 13-2 to 13-5 determine the pressure of the hydraulic cylinder that reduces the rolling segment as L _f
By controlling the static iron pressure + α (0 to 10%) corresponding to the above, it is possible to stably end the casting without causing a steel leak from the top of the slab. In the figure,
L _fo is the length to the crater end, the angle θ at that time
Indicates the angle from the meniscus to the crater end, respectively. Next, the present invention will be described in more detail with reference to examples. EXAMPLE In this example, the present invention was applied to an operation for ending the casting of the unsolidified partial light pressure continuous casting method using equipment similar to the continuous casting equipment shown in FIGS. The casting conditions in this example are as shown in Table 1.
The rolling segment is 1 to 4 segments (13-1 to 13-
5 and 5 segments). At this time, the length L up to the crater end portion at a casting speed of 4 m / min is as described above.
From equation (3), it is obtained as follows. [Equation 5] At this time, 4.6 m was reduced by 30 mm in total of the three reduction segments 13-2 to 13-4 existing on the exit roll side of the four segments 13-4. FIG. 4 is a graph showing the position of the crater end portion during rolling down and the position of the crater end portion during opening in the present example. FIG. 5 is a graph showing the state of deceleration before the end of casting in this example. In this example, based on the above conditions, the effects of the present invention were confirmed by the following examples. Embodiment 1 In this embodiment, an example in which the casting is finished at a steady casting speed (Vc) of 4 m / min. When the residual molten steel in the tundish of the pre-installed upper controller program reaches a predetermined amount,
At the same time as the casting speed is reduced (deceleration α = 4 m / min ² ), a predetermined pressure command is given to the pressure reduction segments 13-1 to 13-4, so that each cylinder of the pressure reduction segment
The position reduction sensor incorporated in 14 detects the amount of reduction per time and feeds it back to reduce the amount by considering the deceleration amount, while the casting speed is Vc = 1.
After the speed reached 5 m / min, the state was reduced by 30 mm only with the reduction segment 13-1 alone. After about 1.2 minutes from this state (solidified slab 17
(The time required for the crater end portion to stably exist in the reduction segment 13-1 is 1.2 minutes or more.) Hot water supply into the mold and after about 10 seconds, remove the reduction segment 13-1.
At the same time as releasing at a release speed of 5 mm / sec, each rolling segment after the rolling segment 13-2 is subjected to the static iron pressure (p = ρHρ
ρ · L _fo sin θ (see FIG. 3), the hydraulic pressure was reduced to 1.1 times the hydraulic pressure equivalent to the overhanging force, whereby a space 25 surrounded by a solidified shell in the mold of the present invention could be created. . The unsolidified molten steel is completely solidified by cooling from the secondary cooling water during the drawing at a speed of (1.5 m / min) for about 2 to 2.6 minutes and then accelerated at an acceleration α = 4 m / min ^2. Vc
= 4 m / min, and the slab could be drawn without causing a single drop of steel leakage. Embodiment 2 This embodiment shows an example in which the casting speed of Embodiment 1 is further reduced from 1.5 m / min to 1 m / min. Also in this example, as in the first embodiment, the length of the unsteady portion slab at this time, that is, the reduction segment
The length from the slab to the final end of the area where bulging is only performed by opening 13-1 is Vc = 1.5 m / min.
At 4.0 m and Vc: 1 m / min, the casting was completed quickly and reliably within less than Max 2.8 m without much difference from the conventional method. [Table 1] According to the casting termination method of the present invention, the casting speed is set to 0.2 at the time of the termination of the casting by the casting method in which the unsolidified portion is reduced, as in the conventional method (see JP-A-6-226414). m /
The casting could be completed while drawing at a relatively high speed without dropping to less than a minute and without installing a cooling box such as a metal frame, thereby further improving productivity.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of an unsolidified rolling continuous casting facility to which the present invention can be applied. FIG. 2 is an explanatory view showing a rolling-down state before completion of casting in the equipment of FIG. FIG. 3 is an explanatory view showing a state in which a short side surface is not fully pressed down and is opened by a pressing reaction force by opening a pressing segment 13-1 after completion of casting. FIG. 4 is a graph showing the position of a crater end during unsolidified rolling casting and opening. FIG. 5 is a graph showing a relationship between a change in casting speed and time at the end of the last stage of casting according to the present invention. [Description of Signs] 10: Pinch rolls 13-1 to 13-5: Roll-down segment 15: Roll-down segment fixed frame 16: Roll-down segment movable frame 18: Cast piece (after solidification) 20: Lower roll fixed frame 19, 22: Pinch roll pressing cylinder 27: Foot roll at the bottom of the mold

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-7-223053 (JP, A) JP-A-4-33757 (JP, A) JP-A-6-226414 (JP, A) JP-A-6-226414 335759 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B22D 11/10 B22D 11/128 350 B22D 11/16 B22D 11/20

Claims (1)

(1) A method for terminating casting while continuously drawing a slab obtained while solidifying molten steel in a mold, comprising: To complete the hot water supply of molten steel, first reduce the casting speed, and then forcibly crush the slab in the thickness direction with a reduction segment arranged directly below or below the mold, from the top of the slab.
The Rukoto molten steel that is overflowing upward into contact with the mold walls
Thus, while the slab is within the mold, molten steel unsolidified within
Producing a solidified wall having a top and a slab top
Before the slab that produced the solidified wall did not fall out of the mold,
The level of the molten steel inside the solidified wall is reduced by returning the rolled-down segment obtained by crushing the cast slab and bulging the cast slab in contact with the rolled-down segment.
In the continuous casting please allowed to consist this <br/> and forming a space in the interior of at least the coagulation wall, makes it possible to pull out the cast slab uppermost top without leakage steel from slab outermost top from the mold Casting termination method.