JP2006239769A - Continuous casting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To expand the installing pitch of narrow face support rolls in a range where the generation of bulging causing internal cracks can be evaded. <P>SOLUTION: Narrow face support rolls 9 are arranged in a range from the lower edge of a mold 3 to at least 2.5 m on the downstream side. The installing pitch of the narrow face support rolls 9 in the above range is set so as to be larger than the installing pitch of wide face support rolls 8, and be smaller than the value prescribed by the distance from the lower edge of the mold 3 to the intermediate point between the mutually adjacent narrow face support rolls 9 as the objects. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a continuous casting apparatus that continuously casts slabs and blooms (slabs).

Conventionally, in a continuous casting apparatus that continuously casts a slab such as a slab or a bloom having a relatively large thickness, several narrow surface support rolls are provided below the mold, and the narrow surface support rolls pull from the mold. A narrow surface of the slab immediately after being extracted is supported (for example, see Patent Document 1).
In such a continuous casting apparatus, the narrow surface support roll has not been studied in detail so far, and when the casting speed is increased or the slab size is increased in order to improve the production efficiency of the slab, With such a few narrow-surface support rolls, bulging that occurs on the narrow surface of the slab cannot be sufficiently suppressed, and internal cracks due to the bulging may occur.

Thus, for example, Patent Document 2 proposes a continuous casting apparatus in which a drum-shaped narrow surface support roll is provided over a range of 6 m from immediately below the mold (immediately before the straightening machine).
JP 59-185559 A JP-A-6-142862

However, in the continuous casting apparatus of Patent Document 2, since the installation pitch of the narrow support rolls is 200 mm, which is the same as the installation pitch of the wide support rolls, the gap between the narrow support rolls is small, and the narrow surface of the slab is reduced. It is difficult to insert a cooling spray for blowing cooling water into the gap. In addition, even when a cooling spray is inserted into the gap, most of the cooling water ejected from the cooling spray will be sprayed on the surface of the narrow support roll, so that the narrow surface of the slab can be efficiently cooled. I can't.
Bulging as described above can be suppressed to such an extent that internal cracks are suppressed by controlling the surface temperature of the slab. Therefore, by setting the installation pitch of the narrow surface support roll as large as possible, the area where the cooling water of the cooling spray can be directly sprayed is expanded on the narrow surface of the slab, thereby narrowing the narrow surface of the slab. It is desirable to make the temperature control of the system more accurate.

On the other hand, since bulging is a phenomenon in which the slab swells between the rolls, setting the installation pitch of the narrow support rolls large without limitation leads to the occurrence of large bulging that causes internal cracks.
Accordingly, an object of the present invention is to increase the installation pitch of the narrow surface support rolls in a continuous casting apparatus within a range in which the occurrence of bulging that causes internal cracks can be avoided.

In order to achieve the above object, the present invention takes the following technical means.
That is, the technical means for solving the problems in the present invention include a wide-surface support roll that supports the wide surface of the slab drawn from the mold and a narrow-surface support roll that supports the narrow surface of the slab on the downstream side of the mold. In a continuous casting apparatus in which a drawing roll for continuously extracting a slab from the mold is provided on the downstream side of the wide surface and narrow surface support rolls,
The narrow surface support roll is disposed in a range from the lower end of the mold to a position at least 2.5 m downstream from the lower end of the mold in order to avoid internal cracks on the narrow surface side of the slab, and the installation pitch of the narrow surface support roll is: It is set to be larger than the installation pitch of the wide surface support rolls and smaller than a value defined based on the distance from the lower end of the mold to each narrow surface support roll.

The direction in which the slab moves from the mold to the drawing roll is the drawing direction of the slab, the mold side is the upstream side, and the drawing roll side is the downstream side with respect to the drawing direction.
Since slab bulging occurs most prominently in the slab immediately after being pulled out of the mold, the slab bulging is suppressed by supporting the slab accurately immediately after the downstream side of the mold. can do. The inventor of the present application provided the narrow surface support roll at the above-mentioned installation pitch in the range from the lower end of the mold to the position at least 2.5 m downstream, thereby causing the bulging of the narrow surface of the slab to cause internal cracking. We know that it can be suppressed to the extent that it does not become.

In addition, the slab drawn from the mold is gradually solidified from the surface toward the inside in the process from the mold to the drawing roll. In the unsolidified slab in this process, a solidified shell having been solidified is formed in an outer shell shape, and unsolidified molten steel exists inward of the solidified shell.
In such an unsolidified slab, the solidified shell is subjected to static pressure from the molten steel (molten steel static pressure), particularly in the initial stage of being pulled out of the mold, and this causes the slab to swell from between the rolls (bulging). Occurs.

  As a result of repeated experiments on bulging generated on the narrow surface of the slab, the inventors of the present application have determined that the installation pitch of the narrow surface support roll of the slab is larger than the installation pitch of the wide surface support roll as shown in the following equation (i). It was discovered that even when set large, the bulging of the narrow surface of the slab can be suppressed to such an extent that internal cracks do not occur.

However, if the installation pitch of the narrow support rolls is set to be large without limitation, it is clear that bulging that causes internal cracks occurs between the rolls of the narrow support rolls.
Therefore, the inventors of the present application, by repeating the experiment, select the distance from the lower end of the mold to each narrow surface support roll as a variable in defining the installation pitch of the narrow surface support roll, and the installation pitch is determined by the variable. It has been discovered that by setting the value smaller than the prescribed value, bulging that occurs between narrow surface support rolls can be suppressed to the extent that internal cracks do not occur. Therefore, by setting the installation pitch of the narrow surface support rolls within such a range, the occurrence of internal cracks due to bulging on the narrow surface side of the slab is avoided.

  More specifically, it is preferable that the installation pitch of the narrow surface support rolls satisfies the following formula (1).

  The inventors of the present application further set an installation pitch of the narrow surface support roll to be smaller than a value defined by using the distance from the lower end of the mold to the middle point of the adjacent narrow surface support roll as a variable by further experimenting. In other words, it was discovered that bulging generated between the rolls can be suppressed to such an extent that internal cracks do not occur, and by setting the installation pitch of the narrow surface support rolls within a range that satisfies the formula (1), The occurrence of internal cracks due to bulging on the narrow side of the piece can be avoided.

More preferably, it is desirable that the narrow surface support roll is disposed in the range from the lower end of the mold to the distance L ₁ calculated by Expression (2) from the downstream side.

The molten steel starts to solidify near the meniscus position immediately after being poured into the mold, and the solidified shell of the slab is formed from the meniscus position. The present inventor has solidified from the lower end of the slab mold by being withdrawn to the position of L ₁ of formula as defined (2) by the meniscus position, until solidified shell capable of holding the molten steel static pressure the thickness of the template piece I have discovered through experiments.
Therefore, by arranging the narrow surface support roll from the lower end of the mold to the position of L ₁ at the above-mentioned installation pitch, bulging of the narrow surface of the slab can be suppressed to the extent that no internal crack occurs.

In addition, bulging is closely related to the surface temperature of the slab, and when the installation state of the narrow support roll is specified by paying attention to the surface temperature, the range from the lower end of the mold to the position 4 m downstream is defined. The narrow surface support roll placement zone is set, the range from the position to the drawing roll is set to the narrow surface support roll non-position zone, and the surface temperature of the narrow surface of the slab passing through the narrow surface support roll non-placement zone is set. It is preferable to maintain the temperature below 1030 ° C.
By passing through the narrow support roll arrangement zone, a slab having a narrow surface in which bulging is suppressed to such an extent that internal cracks do not occur is formed. The inventors of the present application have found by experiment that it is necessary and sufficient to set a range from the lower end of the mold to the position 4 m downstream as the narrow surface support roll arrangement zone where such a slab is formed. ing.

By the way, a narrow surface support roll supports in the state which pinched the slab. For this reason, when the narrow surface of the slab that has passed through the narrow surface support roll arrangement zone is sandwiched again by the narrow surface support roll, the bulging caused by bulging is pushed inward of the slab, thereby narrowing the slab. There is a risk of internal cracks occurring on the surface side.
Therefore, the narrow surface support roll placement zone is set as the narrow surface support roll non-placement zone, and the slab after passing through the narrow surface support roll placement zone is pulled out without the support of the narrow surface support roll. An external force does not act, thereby avoiding internal cracks on the narrow surface side of the slab.

On the other hand, in the narrow surface support roll non-arrangement zone, since the narrow surface of the slab is not supported by the narrow surface support roll, the narrow surface of the slab may swell outward due to the molten steel static pressure.
Therefore, the inventors of the present application suppress the swelling of the narrow surface by keeping the surface temperature of the narrow surface of the slab passing through the narrow surface support roll non-arrangement zone low. The inventors of the present application have found that the swelling as described above can be suppressed by keeping the surface temperature at 1030 ° C. or lower.

Therefore, by maintaining the surface temperature of the narrow surface of the slab passing through the narrow surface support roll non-arrangement zone at 1030 ° C. or less, the swell of the narrow surface of the slab is a cause of quality deterioration of the slab after casting. It can be suppressed to such an extent that it does not become.
From the same viewpoint, and sets the range from the lower end of the mold to a position of a distance L ₁ defined by the formula (2) on the downstream side in Semamen support roll arranged zones, ranging from the position to the withdrawal roll Is set in the narrow surface support roll non-arrangement zone, and the surface temperature of the narrow surface of the slab passing through the narrow surface support roll non-arrangement zone is maintained at 1030 ° C. or less, thereby suppressing the occurrence of internal cracks. The slab is manufactured.

  According to the continuous casting apparatus of the present invention, the installation pitch of the narrow surface support rolls can be expanded within a range in which the occurrence of bulging that causes internal cracks can be avoided.

Hereinafter, embodiments of a continuous casting apparatus according to the present invention will be specifically described with reference to the drawings.
<First Embodiment>
FIG. 1 shows a first embodiment of the present invention.
The continuous casting apparatus 1 according to the present embodiment includes a tundish 2, a mold 3, a support roll 4, a cooling spray 5, and a drawing roll 6.
In the present embodiment, as indicated by an arrow in the figure, the direction drawn by the drawing roll 6 from the mold is the drawing direction of the slab C, the mold side in the drawing direction is the upstream side, and the drawing roll The side is the downstream side.

The tundish 2 is formed in an upwardly open box shape so as to store molten steel H poured from a ladle (not shown). The molten steel H is poured into the bottom of the tundish 2 toward the mold 3. An immersion nozzle 7 is attached.
The mold 3 is provided below the tundish 2 and casts the molten steel H injected from the tundish 2 into a slab C, and is a cylindrical shape in which a hollow portion having a rectangular cross section is formed in a vertically open shape. The length is set to 500 mm to 1500 mm.
The support roll 4 extends downstream from the lower end of the mold to support the slab C. The support roll 4 supports the slab C on the wide surface side of the slab C drawn from the mold 3, and the slab C. And a narrow surface support roll 9 for supporting the narrow surface.

The wide surface support roll 8 is pivotally supported on a rotation axis perpendicular to the drawing direction of the slab C drawn from the lower end of the mold 3. Further, the wide surface support roll 8 facing one wide surface of the slab C and the wide surface support roll 8 facing the other wide surface are opposed to each other. The drawing roll 6 is provided at an installation pitch that can suppress wide-surface bulging.
The narrow surface support roll 9 is pivotally supported by a rotation axis perpendicular to the drawing direction. Further, the narrow surface support roll 9 facing one narrow surface of the slab C and the narrow surface support roll 9 facing the other narrow surface are opposed to each other. It is arranged from the lower end of the casting mold 3 in the drawing direction at the installation pitch described later.

The cooling spray 5 is disposed between the rolls of the support roll 4 in order to spray cooling water onto the slab C.
The drawing roll 6 is disposed downstream of the support roll 4 and continuously draws the slab C from the mold 3. The drawing roll 6 has a rotation axis perpendicular to the drawing direction, and has a pair of wide surfaces of the slab C. It is deployed up and down to pinch. Further, one drawing roll 6 is fixed, and the other drawing roll 6 is configured to be pressed against a wide surface of the slab C to be contacted with a certain pressure by hydraulic pressure or the like.

The molten steel H carried by the ladle is poured into the tundish 2, and the molten steel H stored in the tundish 2 is injected into the mold 3 while the flow rate is controlled by the immersion nozzle 10 at the bottom of the tundish 2. The The molten steel H injected into the mold 3 is solidified by cooling (primary cooling) the contact portion with the inner wall surface of the mold 3, thereby providing a solidified shell S on the surface portion. An unsolidified slab C surrounded by H is formed. The slab C is continuously drawn from the lower end of the mold 3 by the drawing roll 6.
The unsolidified slab C drawn from the lower end of the mold 3 is drawn to the drawing roll 6 while being supported by the support roll 4. At this time, the slab C is cooled (secondary cooling) by the cooling spray 5, whereby solidification of the slab C gradually proceeds from the surface to the inside. Further, the slab C is gradually bent in the process from the lower end of the mold 3 to the drawing roll 6 by the guide of the support roll 4, and in the horizontal direction on the upstream side of the drawing roll 6, solidification is completed. The slab C that has been solidified is cut into a necessary size by a cutting means (not shown) after passing through the drawing roll 6.

As shown in FIG. 3, the unsolidified slab C passing between the support rolls 4 has a solidified shell S that has been solidified as an outer shell, and the solidified shell S is formed of unsolidified molten steel H. Besieged. Further, between the solidified shell S and the unsolidified molten steel H, there is a solid-liquid interface i in which the solid phase ratio of the molten steel H is 1.0 or less.
In the unsolidified slab C immediately after being drawn out of the mold 3, the solidified shell S has a small thickness as shown in FIG. In response to this, the slab C swells outward, thereby causing a phenomenon (bulging) in which the slab C swells between the rolls of the support roll 4.

Further, the swell of the slab C is pressed by the roll as the slab C moves in the drawing direction as indicated by an arrow in the drawing. As a result, a tensile force acts on the inside of the solidified shell S that faces the roll, and a crack (internal crack) is generated inside the solidified shell S by the tensile force.
As described above, large bulging causes internal cracks, and suppressing bulging leads to avoiding the occurrence of internal cracks. For the purpose of suppressing the occurrence of bulging, it has been conventionally practiced to reduce the installation pitch of the support rolls and arrange the support rolls densely.

On the other hand, it is known that bulging can be suppressed by controlling the surface temperature of the slab C. From this viewpoint, the cooling spray 5 for controlling the surface temperature of the slab C and the slab C It is desired to enlarge the area in which the cooling water of the cooling spray 5 can be directly sprayed by enlarging the facing area, and thereby accurately control the surface temperature of the slab C.
As a result of repeated experiments regarding bulging of the narrow surface of the slab C, the inventors of the present application have found that the slab C can be formed even when the installation pitch of the narrow surface support roll 9 is set larger than the installation pitch of the wide surface support roll 8. It was discovered that narrow bulging can be suppressed to the extent that it does not cause internal cracking.

  Thereby, the following formula (i) is established for the installation pitch of the narrow support roll 9 and the wide support roll 8.

On the other hand, when the installation pitch of the narrow surface support roll 9 is set to be large without limitation, bulging that causes internal cracks occurs on the narrow surface of the slab C, thereby forming internal cracks on the narrow surface side of the slab C. Obviously it will be done.
Therefore, the inventors of the present application conducted the following experiment in order to examine the relationship between the internal crack caused by bulging and the installation pitch of the narrow support roll 9.
[Experiment 1]
In a continuous casting apparatus for continuously casting a slab C having a wide surface width of 600 mm and a narrow surface width of 400 mm, 1 m downstream from the lower end of the mold 3 among the wide surface support roll 8 and the narrow surface support roll 9 arranged in a known arrangement state. The installation pitch of the narrow surface support rolls 9 at the position is set to 200 mm, and the cast piece C is continuously cast.

And the cross-sectional sample of this slab C is extract | collected by cut | disconnecting the slab C after casting by a surface perpendicular | vertical to the drawing direction. In the cross-sectional sample, the solidified shell is formed in a layered shape from the outer edge toward the central portion. Therefore, by measuring the distance from the outer edge of an arbitrary point on the cross-sectional sample, the arbitrary point is removed from the lower end of the mold 3. It is possible to specify how much the solidified position at the extracted position.
By using this means, the position of 1 m downstream from the lower end of the mold 3 is specified on the cross-sectional sample, the corresponding position is set as the inspection position, and the inspection position is inspected, whereby the slab at the position 1 m downstream. Check for C internal cracks.

A similar test is performed when the installation pitch of the narrow support roll 9 at a position 1 m downstream from the lower end of the mold 3 is set in increments of 50 mm between 200 mm and 400 mm, and each cross-section sample is inspected.
Next, each of the cross-sectional samples is inspected when the installation pitch of the narrow support rolls 9 located 2 m downstream from the lower end of the mold is set in steps of 50 mm between 300 mm and 450 mm.
Such a test is performed when the installation pitches of the narrow support rollers 3 m, 4 m, and 5 m downstream from the lower end of the mold are appropriately set, and each cross-sectional sample is inspected. The results of these tests are shown in FIG.

In this experiment, the wide-surface support roll 8 and the narrow-surface support roll 9 in a known installation state are arranged from the lower end of the mold 3 to a position where the occurrence of bulging that causes internal cracking can be reliably suppressed. Therefore, the installation pitch can reliably suppress the occurrence of bulging. More specifically, a roll having a roll diameter of 180φ to 300φ is employed, and the installation pitch of the wide surface support rolls 8 is set to about 180 mm to 300 mm.
The casting speed V of the slab C is set to V = 2.0 (m / min), and the surface temperature of the narrow surface of the slab C is maintained at 1000 ° C. to 1230 ° C.

One cooling spray 5 is provided between each roll, and the cooling capacity of each cooling spray 5 is 0.1 to 0.3 ton / hr with respect to V = 0.9 (m / min). Is adopted.
In addition, the steel types of the slab C used in the test are C = 0.12%, 0.4% and 0.6%, and FIG. 4 shows an example result. .
The “under-mold distance (m)” in FIG. 4 indicates the distance from the lower end of the mold 3 at each position. Further, these positions are intermediate points of the narrow surface support rolls 9 adjacent to each other.

The “narrow surface roll pitch (mm)” indicates the installation pitch of the narrow surface support rolls 9.
In addition, in the figure, ◯ indicates that no internal crack was detected from the part corresponding to the corresponding inspection position on the cross-sectional sample even when the installation pitch of the narrow surface support rolls 9 was set as a set value. △ indicates that only 3 or less internal cracks having a length of 2 mm or less occurred at the site corresponding to the corresponding inspection position on the cross-section sample when the installation pitch of the narrow surface support rolls 9 was set as a set value. X in the figure indicates that more than three internal cracks having a length of more than 2 mm occurred at the site corresponding to the corresponding inspection position on the cross-sectional sample when the installation pitch of the narrow surface support rolls 9 was set as a set value. It is shown that.

In addition, although-in the figure indicates that the test was not performed, from other inspection results, as shown in the figure, (◯) (no internal crack) or (×) (internal crack larger than 2 mm) It is estimated that more than 3 occur).
FIG. 5 is a graph showing the results of the experiment shown in FIG. In the graph shown in the figure, the horizontal axis is set to the distance below the mold, and the vertical axis is set to the narrow roll pitch.
As shown in the graph, the boundary between the installation pitch of the narrow surface support rolls 9 that generate internal cracks and the installation pitch of the narrow surface support rolls 9 that do not generate internal cracks is the next variable from the distance from the lower end of the mold 3. Indicated by the formula.

  Therefore, by setting the installation pitch of the narrow surface support rolls 9 at each position in a range that satisfies the following formula (ii), there is no possibility that an internal crack due to bulging occurs on the narrow surface side of the slab C.

  Therefore, by setting the installation pitch of the narrow surface support roll 9 within the range of the following formula (1) derived from the formula (i) and the formula (ii), the internal cracks on the narrow surface side of the slab C can be reduced. The installation pitch of the narrow support rolls 9 can be set larger than the installation pitch of the wide support rolls 8 while suppressing the occurrence.

Further, the narrow surface support roll 9 is positioned at the position immediately after the downstream side of the mold where bulging is most noticeable, more specifically, within the range from the lower end of the mold 3 to the position of at least 2.5 m downstream. It has been experimentally found that it is preferable to be deployed at the installation pitch shown in 1).
According to the continuous casting apparatus of the present embodiment, the slab C drawn out from the mold 3 has an installation in which the narrow surface has a range from the lower end of the mold 3 to a position of at least 2.5 m expressed by the formula (1). By being supported by the narrow surface support rolls 9 arranged at a pitch, there is no possibility that internal cracks due to bulging occur on the narrow surface side of the slab C.

Therefore, the installation pitch of the narrow surface support rolls 9 can be set within a range satisfying the expression (1), and thereby, the opposing region between the narrow surface of the slab C and the cooling spray 5 that should cool the narrow surface. Therefore, the control of the surface temperature of the narrow surface of the slab C is more accurately performed. As a result, bulging is more accurately controlled and the quality of the slab C is improved.
<Second Embodiment>
FIG. 6 shows a second embodiment of the present invention.

Since bulging that causes internal cracks is caused by deformation of the solidified shell S due to the hydrostatic pressure of the molten steel, the internal cracks are prominently generated in the solidified shell S that is solidified immediately after being pulled out of the mold 3. Then, since the solidified shell S is formed to a sufficient thickness as the slab C is cooled, deformation of the solidified shell S due to the molten steel static pressure becomes slight, and thus the solidified shell S is formed. There is no risk of internal cracks occurring in the slab C.
Thus, in the present embodiment, the narrow surface of the slab C is supported by the narrow surface support roll 9 so that the thickness of the solidified shell S of the slab C can avoid the occurrence of internal cracks. For the purpose of reaching the position, by defining the position from the meniscus position of the molten steel H, an arrangement method of the narrow surface support roll 9 for more reliably preventing the occurrence of internal cracks is employed.

Prior to setting the range in which the narrow surface support roll 9 is deployed in the present embodiment, Experiment 2 shown below was performed in order to examine the relationship between the deployment state of the narrow surface support roll 9 and the occurrence of internal cracks.
[Experiment 2]
In a continuous casting apparatus for continuously casting a slab C having a wide surface width of 600 mm and a narrow surface width of 400 mm, of the wide surface support roll 8 and the narrow surface support roll 9 arranged in a known arrangement state, 2 m downstream from the lower end of the mold 3. The installation pitch of the narrow surface support rolls 9 at the position is set to 400 mm, and the slab C is continuously cast.

Thereafter, a cross-section sample is taken from the slab C as in Experiment 1, and a position 2 m downstream from the meniscus position is specified on the cross-section sample, the corresponding position is set as the inspection position, and an internal crack is present at the inspection position. Check to see if it has occurred.
A similar test is performed when the installation pitch of the narrow surface support roll 9 at a position 2 m downstream from the lower end of the mold 3 is set between 400 mm and 800 mm in increments of 100 mm, and each cross-section sample is inspected.
Such a test is performed when the installation pitch of the narrow surface support rolls 4 m, 6 m, 8 m and 10 m downstream from the lower end of the mold is appropriately set, and each cross-sectional sample is inspected. The results of these tests are shown in FIG.

In this experiment, the casting speed V is set to V = 1.0 (m / min), and other conditions are the same as those in Experiment 1.
In FIG. 7, “meniscus distance (m)” indicates the distance from the meniscus position to each position, and “solidified shell thickness (mm)” corresponds to the solid phase ratio fs = 0.8 at each position. The thickness of the solidified shell S to be calculated is calculated.
The “narrow surface roll pitch (mm)” indicates the installation pitch of the narrow surface support rolls 9. In the figure, ◯, Δ, and X indicate the same contents as in FIG.

The “narrow surface slab narrow surface temperature” indicates the surface temperature of the narrow surface of the slab C at each position.
As shown in FIG. 7, on the narrow surface side of the slab C, when the thickness of the solidified shell S corresponding to the solid phase ratio fs = 0.8 reaches about 60 mm, regardless of the installation pitch of the narrow surface support rolls 9. It turns out that an internal crack does not occur on the narrow surface side of the slab C.
By the way, the thickness of the solidified shell S is defined by the following formula (iii).

  From the formula (iii), the position where the thickness of the solidified shell S reaches 60 mm from the meniscus position of the molten steel H is given by the following formula (iv).

  Further, assuming that the solidification of the slab C is completed at the position of the drawing roll 6, the Vc (m / min) is given by the following formula (v) from the formula (iii).

  By eliminating Vc from the above formulas (iv) and (v), the following formula (vi) is given.

Since the thickness of the solidified shell S of the slab C at the position advanced by the formula (vi) downstream from the meniscus position becomes 60 mm, the narrow surface support roll 9 narrows the mold 3 from the lower end of the mold 3 to the position. If the surface is supported, there is no possibility of internal cracks due to bulging occurring on the casting surface side of the mold 3. That is, in the continuous casting apparatus 1, in order to secure a predetermined solidified shell thickness, the narrow surface support roll 9 is provided from the meniscus position to the position of the maximum downstream side L _O , and thereafter is not necessary. Means.

Accordingly, the narrow surface support roll 9 is installed at the installation pitch given by the above equation (1) in the range from the lower end of the mold 3 to the downstream side at the position where the distance L ₁ is calculated by the following equation (2). That's fine.

According to the continuous casting apparatus of the present embodiment, the slab C drawn from the mold 3 has a range from the lower end of the mold 3 to the position where the slab C has advanced to the formula (2) by the formula (1). By being supported by the narrow surface support rolls 9 arranged at the installation pitch, the occurrence of internal cracks on the narrow surface side of the slab C is more reliably suppressed.
<Third Embodiment>
FIG. 8 shows a third embodiment of the present invention.

The narrow surface support roll 9 supports the narrow surface of the cast slab C to suppress the swelling of the narrow surface, and also contributes to internal cracks by pressing the bulging formed between the rolls.
Further, the swelling of the slab C and the surface temperature of the slab C are closely related to each other, and the narrow surface of the slab C is supported by the narrow surface support roll 9 by keeping the surface temperature of the narrow surface low. Even when there is no swell, the bulge of the narrow surface can be suppressed.
Therefore, in the present embodiment, in view of the fact that the narrow surface of the slab C is supported by the narrow surface support roll 9 contributes to the internal crack on the narrow surface side of the slab C. An object of the present invention is to provide a region in which the narrow surface of C is not supported by the narrow surface support roll 9 and to keep the surface temperature of the narrow surface of the slab C passing through the region low, thereby suppressing swelling in the region.

That is, in the present embodiment, the range of the downstream side 4m of the mold 3 is set to the narrow surface support roll arrangement zone 11 in which the narrow surface support rolls 9 are arranged at the installation pitch of the above formula (1), and from this position. The range up to the drawing roll 6 is set to the narrow surface support roll non-arrangement zone 12 where the narrow surface support roll 9 is not provided, and the surface temperature of the narrow surface of the slab C in the narrow surface support roll non-arrangement zone 12 is set to a certain specific value. By maintaining the temperature below the temperature, swell of the slab in the narrow surface support roll non-arrangement zone 12 is suppressed.
The inventor of the present application detects the surface temperature of the narrow surface of the slab C and the swelling of the narrow surface (center deformation amount) when the narrow surface of the slab C is not supported by the narrow surface support roll 9 in order to detect the specific temperature. The following experiment was conducted to investigate the relationship.
[Experiment 3]
When continuously casting a slab C having a wide surface width of 600 mm and a narrow surface width of 400 mm using the continuous casting apparatus 1, a wide surface support roll with a known installation pitch in a range from the lower end of the mold 3 to a position advanced 4 m downstream. 8 and the narrow surface support roll 9 are disposed, and the narrow surface support roll 9 is not disposed between the position and the drawing roll 6, and the slab C is cast in this state.

Then, the surface temperature and the central deformation amount of the narrow surface of the slab C at the position on the upstream side of the drawing roll 6 were measured, and the central deformation amount at each surface temperature is shown in FIG.
In this experiment, the casting speed V is set to V = 2.0 (m / min), and other conditions are the same as those in Experiment 1.
FIG. 10 is a graph of FIG. 9, in which the horizontal axis indicates the surface temperature of the narrow surface of the slab C, and the vertical axis indicates the central deformation amount of the narrow surface of the slab C.
By the way, it is known that if the center deformation amount of the narrow surface of the slab C is 8.0 mm or less, there is no problem in the quality of the slab C after casting.

As shown in the graph of FIG. 10, the surface temperature of the narrow surface of the slab C where the center deformation amount of the narrow surface of the slab C is 8.0 mm is 1030 ° C.
Therefore, in the present embodiment, by maintaining the surface temperature of the narrow surface of the slab C in the narrow surface support roll non-arrangement zone 12 at 1030 ° C. or less, the slab of the slab in the narrow surface support roll non-arrangement zone 12 is maintained. The swelling of the narrow surface does not become larger than 8.0 mm, which is a problem in terms of products.
<Fourth embodiment>
FIG. 11 shows a fourth embodiment of the present invention.

The fourth embodiment is a modification of the third embodiment.
In other words, in the fourth embodiment, the narrow surface support roll 9 is provided in the range from the lower end of the mold 3 to the position indicated by the above formula (2) at the downstream side at the installation pitch of the above formula (1). The narrow surface support roll arrangement zone 11 is set, and the range from the position to the drawing roll 6 is set to the narrow surface support roll non-arrangement zone 12 where the narrow surface support roll 9 is not provided.
Moreover, the surface temperature of the narrow surface of the slab C in the narrow surface support roll non-arrangement zone 12 is maintained at 1030 ° C. or lower as in the third embodiment.

In the third or fourth embodiment, the slab passes through the narrow surface support roll arrangement zone 11 at the initial drawing stage where the solidified shell S is not formed with a sufficient thickness, thereby suppressing bulging. The solidified shell S is formed to a thickness capable of supporting the molten steel static pressure.
Then, the slab C provided with the solidified shell S passes through the narrow surface support roll non-arrangement zone 12 after passing through the narrow surface support roll arrangement zone 11. At this time, since the pressing force by the narrow surface support roll 9 does not act on the narrow surface of the slab C, the occurrence of internal cracks due to the pressing force is avoided.

At this time, it is considered that the narrow surface of the slab C swells outward due to the molten steel static pressure, but the surface temperature of the narrow surface of the slab C in the narrow surface support roll non-arrangement zone 12 as in the above embodiment. By keeping the temperature at 1030 ° C. or lower, the bulge of the narrow surface of the slab C in the narrow surface support roll non-arrangement zone 12 can be suppressed to such an extent that the quality after casting does not become a problem.
Therefore, according to the third and fourth embodiments, a high-quality slab C that does not have an internal crack and suppresses the swelling of the narrow surface is cast.
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments. For example, the present invention can be employed in a continuous casting apparatus such as a vertical type or a curved type. Moreover, it is also possible to employ | adopt for the continuous casting apparatus which casts a slab and billet continuously, and also in this apparatus, the effect similar to this Embodiment is shown.

  Moreover, the upper limit of the installation pitch of the narrow surface support roll is appropriately changed depending on the steel type and size of the cast slab to be cast, the casting speed, the cooling capacity of the cooling spray, etc. By defining the pitch, bulging on the narrow surface side of the slab can be suppressed to such an extent that it does not cause internal cracks.

It is a schematic diagram which shows 1st Embodiment of this invention. It is a schematic diagram which shows a mode that bulging arises in a slab. It is a schematic diagram which shows a mode that an internal crack arises in a slab. It is the figure which showed the relationship between the distance from the lower end of a casting_mold | template, and the installation pitch of a narrow surface support roll. It is the graph which showed the relationship between the distance from the lower end of a casting_mold | template, and the installation pitch of a narrow surface support roll. It is a schematic diagram which shows 2nd Embodiment of this invention. It is the figure which showed the relationship between the distance from a meniscus position, and the installation pitch of a narrow surface support roll. It is a schematic diagram which shows the 3rd Embodiment of this invention. It is the figure which showed the relationship between the surface temperature of the narrow surface of slab, and the amount of center deformation. It is the graph which showed the relationship between the surface temperature of the narrow surface of a slab, and the amount of center deformation. It is a schematic diagram which shows 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Continuous casting apparatus 2 Tundish 3 Mold 4 Support roll 5 Cooling spray 6 Drawing roll 7 Immersion nozzle 8 Wide surface support roll 9 Narrow surface support roll 11 Narrow surface support roll arrangement zone 12 Narrow surface support roll arrangement zone H Molten steel C Slab S Solidified shell

Claims (5)

On the downstream side of the mold, a wide surface support roll that supports the wide surface of the slab drawn from the mold and a narrow surface support roll that supports the narrow surface of the slab are arranged, and the downstream side of the wide surface and the narrow surface support roll Further, in a continuous casting apparatus in which a drawing roll for continuously extracting a slab from the mold is provided,
The narrow surface support roll is disposed in a range from the lower end of the mold to a position at least 2.5 m downstream from the lower end of the mold in order to avoid internal cracks on the narrow surface side of the slab, and the installation pitch of the narrow surface support roll is: A continuous casting apparatus characterized in that it is set to be larger than the installation pitch of the wide surface support rolls and smaller than a value defined on the basis of the distance from the lower end of the mold to each narrow surface support roll. The continuous casting apparatus according to claim 1, wherein an installation pitch of the narrow surface support rolls satisfies the formula (1).

The narrow face support rolls, according to claim 1 or claim 2, characterized in that it is deployed in a range from the lower end of the mold to the position of the distance L ₁ calculated by equation (2) on the downstream side Continuous casting equipment.

  A range from the lower end of the mold to a position 4 m downstream is set as a narrow surface support roll arrangement zone, and a range from the position to the drawing roll is set as a narrow surface support roll non-position zone, the narrow surface support The continuous casting apparatus according to claim 1 or 2, wherein the surface temperature of the narrow surface of the slab passing through the roll non-arrangement zone is maintained at 1030 ° C or lower. Wherein the lower end of the mold with a range of up to the position of the distance L ₁ as defined in claim 3 on the downstream side is set to a narrow face support roll arranged zones, the range narrow surface from the position to the withdrawal roll support rolls non A continuous casting apparatus characterized in that a surface temperature of a narrow surface of a slab set in an arrangement zone and passing through the narrow surface support roll non-arrangement zone is maintained at 1030 ° C or lower.

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