JP5266154B2 - Rectifying structure that suppresses drift caused by opening and closing of slide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a drift caused by the opening/closing of a slide plate. <P>SOLUTION: The rectifying structure 10 is connected to the downstream side of a slide plate system flow rate regulation unit used in continuous casting, and in which an inner tube shape 11 in the upper edge 11a has a circular shape, the inner tube shape 11 is continuously deformed from the upper edge 11a, and the inner tube shape 11 in the lower edge 11b has a flat shape having a major axis 11y and a minor axis 11x. Then, the minor axis 11a of the inner tube shape 11 in the lower edge 11b is parallel to the opening/closing direction of the slide plate of the flow rate regulation unit, and the part directly below the lower edge 11b is connected with an immersion nozzle in which the shape of the inner tube is the circular one having a diameter more than the major axis 11y of the inner tube shape 11 in the lower edge 11b, and also, a discharge hole for molten steel is made. Further, the length x of the minor axis 11x and the length y of the major axis 11y satisfy 0.5&le;x/y&le;0.8. and further, the distance z from the lower edge of the rectifying structure to the upper edge of the discharge hole for molten steel satisfies 200 mm&le;z&le;900 mm. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a rectifying structure connected to a downstream side of a flow rate adjustment unit of a slide plate type used in continuous casting.

  Conventionally, various techniques have been proposed in which a rectifying structure such as an intermediate nozzle is provided between a flow rate adjusting unit and an immersion nozzle (see, for example, Patent Document 1).

JP 2001-316460 A

  In Patent Document 1, due to the opening and closing of the slide plate of the slide valve (flow rate adjusting unit), the flow of molten steel in the immersion nozzle becomes uneven in the opening and closing direction of the slide plate. For this reason, when the opening and closing direction of the slide plate is the mold width direction, it is connected to the drift in the mold width direction in the mold. When this uneven flow occurs, a strong local flow is generated at the mold corner, which promotes remelting of the shell at the mold corner and causes a solidification delay. As a result, there is a risk of slab breakout.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a rectifying structure capable of suppressing a drift caused by opening / closing of a slide plate.

In order to solve the above problems, the flow straightening structure of the present invention is a flow straightening structure connected to the downstream side of a flow rate adjustment unit of a slide plate type used in continuous casting. The inner tube shape is continuously deformed, the inner tube shape at the lower end is a flat shape having a major axis and a minor axis, and the minor axis of the inner tube shape at the lower end is the opening / closing direction of the slide plate of the flow rate adjusting unit Is connected to a circular pipe part having a diameter equal to or larger than the major axis of the inner pipe shape at the lower end and in which a molten steel discharge hole is drilled. Expressions (1) and (2) are satisfied.
0.5 ≦ x / y ≦ 0.8 (1)
200 mm ≦ z ≦ 900 mm (2)
However,
x is the length of the short axis of the inner pipe shape at the lower end of the rectifying structure y is the length of the long axis of the inner pipe shape at the lower end of the rectifying structure z is the length of the molten steel discharge hole of the circular pipe portion from the lower end of the rectifying structure Distance to top

  In the rectifying structure according to the present invention, as described above, the inner tube shape at the upper end is circular, the inner tube shape is continuously deformed from the upper end, and the inner tube shape at the lower end is a flat shape having a major axis and a minor axis. By doing so, the flow of molten steel gathers at the approximate center in the short axis direction. Here, since the short axis direction is parallel to the opening / closing direction of the slide plate, it is possible to suppress the drift due to the opening / closing of the slide plate.

Overall schematic of continuous casting equipment Diagram showing mold configuration Diagram showing the configuration of the immersion nozzle Sectional drawing of the rectification | straightening structure which concerns on one Embodiment of this invention, a flow volume adjustment unit, and an immersion nozzle The figure which shows the detail of the rectification | straightening structure shown in FIG. Illustration of solidification delay Diagram showing relationship between solidification delay and occurrence of breakout Explanatory drawing for explaining a method for quantifying the drift in the mold width direction Diagram showing the relationship between the degree of solidification delay and the difference Δh Explanatory diagram for explaining the method for quantifying the drift in the mold width direction in the water model Diagram showing measurement points for flow velocities U ₁ , U ₂ , V ₁ , V ₂ Diagram showing the correlation between the degree of drift in the immersion nozzle and the degree of drift in the mold width direction Diagram showing the dimensions of the immersion nozzle A diagram showing the relationship between the degree of drift in the immersion nozzle and the water flow rate The figure which shows the relationship between the degree of drift in an immersion nozzle and the short axis-major axis ratio of the rectifying structure lower end Diagram showing the relationship between the degree of drift in the immersion nozzle and the distance from the bottom of the flow straightening structure to the molten steel discharge hole

  As is well known, when paying attention to the casting path of the continuous casting equipment, there are a curved continuous casting equipment and a vertical bending continuous casting equipment. The former has an arc path section, a correction path section, and a horizontal path section along the casting path from the mold, and the latter has a vertical path section upstream of the arc path section, and floats inclusions in the molten steel. Is intended. Focusing on the cross-sectional shape of the slab cast by the continuous casting equipment, there are slabs having a cross-sectional aspect ratio of 2 or more, blooms of 2 or less, and billets having a square cross-sectional shape. The object of application of the present invention is all the continuous casting equipment listed as described above. Hereinafter, as an example, the present invention will be described by applying the present invention to a vertical bending type continuous casting equipment for slabs. .

  Hereinafter, based on FIGS. 1-3, the continuous casting installation 100, its casting_mold | template 1, and the immersion nozzle 2 are outlined.

  The continuous casting equipment 100 is used for smoothly pouring the molten steel held in the tundish 9 into the mold 1 at a predetermined flow rate by cooling the molten steel to be poured to form a shell having a predetermined shape. An immersion nozzle 2 and a plurality of roll pairs 3 arranged in parallel along the casting path Q from directly below the mold 1 are provided. The configuration of the mold 1 will be described in detail later with reference to FIG. 2, and the configuration of the immersion nozzle 2 will be described in detail later with reference to FIG. In the present embodiment, the casting path Q is provided with a vertical path portion extending in a substantially vertical direction, an arc path portion connected to the vertical path portion and extending in an arc shape, and further provided downstream thereof and extending in the horizontal direction. It consists of a horizontal path | route part and the correction | amendment path | route part for connecting the said circular arc path | route part and a horizontal path | route part smoothly.

  Each of the roll pairs 3 is composed of a pair of rolls 3a and 3a for sandwiching a slab as a casting object with both wide surfaces. The roll gap [mm] as the shortest distance between the roll surfaces of the pair of rolls 3a and 3a is configured to be adjustable by appropriate means.

  Further, in the first half of the casting path Q, a cooling spray 4 for spraying cooling water at a predetermined flow rate on a solidified shell formed in the mold 1 and pulled out from the mold 1 is appropriately provided. In general, the mold 1 is referred to as a primary cooling zone, and in this sense, a path portion where the cooling spray 4 is disposed is referred to as a secondary cooling zone.

  The shell pulled out from the mold 1 and transported along the casting path Q is further cooled and contracted by natural heat radiation, the cooling spray 4 or the like. Therefore, the roll gap [mm] of the roll pair 3 is generally set so as to be gradually narrowed as it proceeds to the downstream side of the casting path Q.

  With the above configuration, in order to start continuous casting of the slab, before pouring molten steel into the mold 1, a dummy bar (not shown) is inserted in the casting path Q in advance and the mold is inserted through the immersion nozzle 2. The molten steel is started to be poured into 1 and the dummy bar is pulled out downstream. The amount of molten steel poured into the mold 1 and the pulling speed of the dummy bar are gradually increased until the casting speed reaches a predetermined casting speed. The dummy bar is collected by an appropriate means when a predetermined meniscus distance is reached. As a result, the slab is continuously cast.

Next, general operating conditions of the continuous casting equipment 100 will be briefly introduced. The following is an example.
-Mold width W [mm] shall be 800-2100.
-Mold thickness T [mm] shall be 230-280.
-Mold height H [mm] shall be 800-1000.
-Casting speed Vc [m / min] shall be 0.8-3.0.
-Molten steel superheat degree (DELTA) T [degreeC] shall be 0-40.
The specific water amount Wt [L / kg Steel] is 0.15 to 3.
-In-mold electromagnetic stirring intensity M-EMS [gauss] shall be 0-1000.
-Molten steel composition is based on an agreement between the parties. Typical components are C, Si, and Mn. To this, Cr, Cu or the like is appropriately added. Contains other inevitable impurities.

Here, each term is briefly explained.
The mold width W [mm] and the mold thickness T [mm] are specified at the upper end of the mold 1 as shown in FIG.
The casting speed Vc [m / min] is a drawing speed of the slab, and is specified by the peripheral speed of the pinch roll 3b of the roll pair 3 arranged in the uppermost stream among the plurality of roll pairs 3.
The molten steel superheat degree ΔT [° C.] is an index of the temperature of the molten steel poured into the mold 1.
The specific water amount Wt [L / kg Steel] means the volume of cooling water used for 1 kg of steel.
In-mold electromagnetic stirring strength M-EMS [gauss] is an index of the strength of the magnetic field applied to stir the molten steel in the mold 1.

<Mold 1>
Next, the structure of the mold 1 will be described with reference to FIG. As shown in FIG. 2A, the mold 1 according to this embodiment is configured for a so-called slab in which a cast slab has a rectangular cross section and an aspect ratio of 2 or more. The mold 1 is opposed to a pair, a wide mold 5 that forms the mold wide surface 1a, and a narrow mold 6 that is disposed between the wide mold 5 and that is opposed to each other to form the mold narrow surface 1b. A mold frame (not shown) that supports the mold 5 and the narrow-face mold 6 is provided as a main configuration.

<Immersion nozzle 2>
Next, the structure of the immersion nozzle 2 will be described with reference to FIG. As shown in FIG. 3A, the immersion nozzle 2 used in the present embodiment has a bottomed cylindrical shape, and a pair of opposed molten steel discharge holes 7 are formed slightly above the inner bottom 8. Two-hole type. As shown in FIG. 3 (b), the pair of molten steel discharge holes 7 has a downward angle θ [deg.] Of the molten steel discharge flow from the molten steel discharge holes 7. ] Is set obliquely downward from the inner periphery to the outer periphery so that it is set to 15 to 45 with respect to the horizontal. This downward angle θ [deg. ] Corresponds in detail to the angle between the lower end line 7a (contour of the lower end) of the molten steel discharge hole 7 and the horizontal specified in the vertical section of the immersion nozzle 2 in this embodiment. And the intersection of this lower end line 7a and the axis 2a of the immersion nozzle 2 is defined as a virtual intersection P.

  As shown in FIG. 2B, the immersion nozzle 2 is set vertically in the mold 1 such that the pair of molten steel discharge holes 7 face the mold narrow surface 1b. In other words, the immersion nozzle 2 is set vertically in the mold 1 so that the flow of molten steel discharged from the pair of molten steel discharge holes 7 is perpendicular to the mold narrow surface 1b in plan view. In this state, when molten steel is poured from the immersion nozzle 2 into the mold 1, the molten steel flow from the immersion nozzle 2 first becomes obliquely downward, and eventually, when it collides with the mold narrow surface 1 b, it branches in the vertical direction. An upward flow Q and a downward flow R are formed. Of these, the upward flow Q plays a role of preventing the so-called skinning in which the surface is solidified by supplying heat to the molten steel near the meniscus.

  Next, a more specific configuration of the continuous casting facility 100 according to the present embodiment will be described. In this continuous casting equipment 100, the amount of molten steel from the tundish 9 to the immersion nozzle 2 is adjusted by the slide plate type flow rate adjusting unit 20, and the mold width caused by opening and closing of the slide plate 22 of the flow rate adjusting unit 20 is adjusted. Directional drift is suppressed by the rectifying structure 10 provided on the downstream side of the flow rate adjustment unit 20.

<Flow adjustment unit 20>
As shown in FIG. 4, a flow rate adjusting unit 20 is provided on the downstream side of the insert nozzle 9 a provided on the bottom surface of the tundish 9. The flow rate adjustment unit 20 is a three-layer flow rate adjustment mechanism including an upper plate 21, an intermediate plate (slide plate) 22, and a lower plate 23. Through holes are formed at substantially the centers of these plates 21 to 23, and the through holes communicate with each other to form a molten steel passage 20a. In the three-layer flow rate adjusting unit 20, the intermediate plate 22 slides with respect to the fixed upper plate 21 and lower plate 23, thereby adjusting the opening degree of the molten steel flow path 20 a formed therein. The amount of molten steel supplied from the immersion nozzle 2 into the mold 1 is controlled. The opening / closing direction of the intermediate plate 22 is parallel to the mold width direction (FIG. 2A).

<Rectifying structure 10>
Next, the rectifying structure (rectifying nozzle) 10 connected to the downstream side of the flow rate adjusting unit 20 will be described in detail. The rectifying structure 10 of the present embodiment is an independent component different from the immersion nozzle 2 and the flow rate adjustment unit 20, but the present invention is not limited to this, and the rectification structure 10 is integrated with the flow rate adjustment unit 20 and the immersion nozzle 2. It may be formed automatically. As shown in FIG. 5, in the rectifying structure 10, the inner tube shape 11 at the upper end 11a is circular, the inner tube shape 11 is continuously deformed from the upper end 11a, and the inner tube shape 11 at the lower end 11b is a short axis. It is a flat shape having 11x and a long axis 11y. The inner tube shape 11 at the upper end 11 a is the same circle as the inner diameter of the flow rate adjusting unit 20, that is, the inner diameter of the through hole of the lower plate 23. The direction of the short axis 11x of the inner tube shape 11 at the lower end 11b of the rectifying structure 10 is parallel to the opening / closing direction of the intermediate plate 22 of the flow rate adjustment unit 20. That is, the direction of the short axis 11x of the inner tube shape 11 at the lower end of the rectifying structure 10 is parallel to the mold width direction (FIG. 2A).

  In the present embodiment, the horizontal cross-sectional area of the inner tube shape 11 of the rectifying structure 10 is set to be substantially the same at each height position. That is, the flow path cross-sectional area of the molten steel passing through the rectifying structure 10 is substantially the same at each height position.

Here, when the length of the short axis 11x of the inner tube shape 11 at the lower end 11b of the rectifying structure 10 is x and the length of the long axis 11y is y, the length x of the short axis 11x and the length of the long axis 11y are set. The flatness “x / y” that is the ratio of the height y satisfies the following formula (1).
0.5 ≦ x / y ≦ 0.8 (1)

The present inventors have found that when the flatness “x / y” is less than 0.5, nozzle clogging is likely to occur in the immersion nozzle 2, so the lower limit is set to 0.5.
In addition, the present inventors have found that when the flatness “x / y” is greater than 0.8, the suppression of drift in the immersion nozzle 2 is extremely deteriorated, so the upper limit is set to 0.8. To do.

Immediately below the lower end 11b of the rectifying structure 10, the immersion nozzle 2 having the circular inner tube shape 2b is connected as shown in FIG. The circular inner tube shape 2b at the upper end of the immersion nozzle 2 has a diameter equal to or greater than the major axis 11y of the inner tube shape 11 at the lower end 11b of the rectifying structure 10, and the inner tube shape 2b of the immersion nozzle 2 is The flow of the molten steel from the flow straightening structure 10 to the immersion nozzle 2 is not obstructed. Here, when the distance from the lower end 11b of the rectifying structure 10 to the upper end of the molten steel discharge hole 7 of the immersion nozzle 2 is z, the distance z satisfies the following formula (2).
200 mm ≦ z ≦ 900 mm (2)
The inner tube shape 2 b of the immersion nozzle 2 extends in the same circular shape from the upper end of the immersion nozzle 2 to the molten steel discharge hole 7.

When the distance z from the lower end 11b of the rectifying structure 10 to the upper end of the molten steel discharge hole 7 of the submerged nozzle 2 is less than 200 [mm], the inventors of the present application extremely deteriorate the suppression of the drift in the submerged nozzle 2. As a result, the lower limit is set to 200 [mm].
Moreover, since the distance z from the lower end 11b of the rectifying structure 10 to the upper end of the molten steel discharge hole 7 of the immersion nozzle 2 is about 1 [m] even if it is long, it is set to 900 [mm] as a practical upper limit. .

[Effect of rectifying structure 10 of this embodiment]
In the present embodiment, as described above, the inner tube shape 11 at the upper end 11a of the rectifying structure 10 is circular, the inner tube shape 11 is continuously deformed from the upper end 11a, and the inner tube shape 11 at the lower end 11b is short. By adopting a flat shape having the shaft 11x and the long shaft 11y, the flow of the molten steel is collected at substantially the center in the direction of the short shaft 11x. Here, since the direction of the short axis 11x is parallel to the opening / closing direction of the intermediate plate (slide plate) 22, the drift in the mold width direction due to the opening / closing of the intermediate plate 22 can be suppressed.

  In the present embodiment, the flatness x / y of the inner tube shape 11 at the lower end 11b of the rectifying structure 10 is set to a range of 0.5 ≦ x / y ≦ 0.8, whereby the submerged nozzle 2 is clogged with nozzles. It is possible to suppress the drift in the mold width direction caused by the opening and closing of the intermediate plate 22 while suppressing the occurrence of.

  In the present embodiment, the distance z from the lower end 11b of the rectifying structure 10 to the upper end of the molten steel discharge hole 7 of the immersion nozzle 2 is set to a range of 200 mm ≦ z ≦ 900 mm, so that the intermediate plate is within a practical range. The drift in the mold width direction due to the opening and closing of 22 can be suppressed.

  Moreover, in this embodiment, the shape of the molten steel flow path from the upper end of the flow straightening structure 10 to the molten steel discharge hole 7 of the immersion nozzle 2 is made circular → elliptical → circular, that is, a part of the molten steel flow path is elliptical. Compared to the case where the elliptical flow path extends to the molten steel discharge hole 7 by adopting the shape, (1) it is possible to suppress the occurrence of drift in the mold width direction, and (2) nozzle clogging occurs. Can be suppressed.

  Hereinafter, the test performed in order to confirm the technical effect of the rectification | straightening structure which concerns on this embodiment is demonstrated. Each numerical range described above is reasonably supported by the following confirmation test. Each of the following tests 1 to 3 is a so-called water model test in which a water tank and water are used instead of the mold and molten steel, and the drift in the immersion nozzle is changed while changing the structure and size of the rectifying structure and the immersion nozzle. The degree was evaluated. In the following tests 1 to 3, when the drift current in the immersion nozzle is less than 0.06, it is evaluated as “◯ (no risk of breakout)”, and the drift current in the immersion nozzle is 0.06 or more. Sometimes it is evaluated as “× (There is a risk of breakout)”. The grounds for setting the drift degree threshold to 0.06 are attached to the end of this specification.

<< Test 1: Relationship between the degree of drift in the immersion nozzle and the flow rate of water >>
In this test, the water flow rate Q of 5000 [cm ³ / s], 8333 [cm ³ / s], 11667 [cm ³ / s], 13333 [cm ³ / s], 15000 [cm ³ / s] is applied to the immersion nozzle. _The degree of drift in the immersion nozzle when _w was supplied was evaluated. Test No. 1 to 4 are comparative examples. 5 to 10 are examples. Each test No. Each test condition of 1-10 and its test result are shown in the following Table 1 and FIG.

Test No. according to the comparative example. In 1-4, the water flow rate _{Q w} applied to the immersion ^{nozzle, 5000 [cm 3 / s]} , 8333 [cm 3 / s], 11667 [cm 3 / s], 13333 [cm 3 / s], 15000 In any case of [cm ³ / s], it can be seen that the degree of drift in the immersion nozzle is 0.06 or more.

On the other hand, test no. In 5-10, the water flow rate _{Q w} applied to the immersion ^{nozzle, 5000 [cm 3 / s]} , 8333 [cm 3 / s], 11667 [cm 3 / s], any of 13333 ^[cm 3 / s] Even in this case, it can be seen that the degree of drift in the immersion nozzle is less than 0.06.

<< Test 2: Relationship between the degree of drift in the immersion nozzle and the ratio of the short axis to the long axis at the bottom of the rectifying structure >>
In this test, the degree of drift in the immersion nozzle was evaluated when the ratio (flatness) x / y between the minor axis and the major axis at the lower end of the rectifying structure was changed. Test No. Examples 11 and 12 are examples. 13 is a comparative example. Each test No. Each test condition of 11-11 and its test result are shown in the following Table 2 and FIG.

  The shape of the lower end of the rectifying structure is an elliptical shape (flat shape), and the flatness x / y value of the elliptical shape is 0.65 and 0.75 (0.5 ≦ x / y ≦ 0.8). Test No. according to Example 11 and 12, it can be seen that the degree of drift in the immersion nozzle is less than 0.06.

  On the other hand, the shape of the lower end of the rectifying structure is circular and the test No. 1 according to the comparative example in which the flatness x / y value is 1. 13, it can be seen that the degree of drift in the immersion nozzle is 0.06 or more.

«Test 3: Relationship between the degree of drift in the immersion nozzle and the distance from the bottom of the rectifying structure to the molten steel discharge hole»
In this test, the degree of drift in the immersion nozzle was measured when the distance z from the lower end of the flow straightening structure to the molten steel discharge hole was changed. Test No. 14 is a comparative example. Examples 15 to 17 are examples. Each test No. Each test condition of 14-17 and its test result are shown in the following Table 3 and FIG.

  Test No. 1 according to a comparative example in which the distance z from the lower end of the rectifying structure to the molten steel discharge hole is 170 mm (less than 200 mm). 14, it can be seen that the degree of drift in the immersion nozzle is 0.06 or more.

  On the other hand, test Nos. According to the examples in which the distance z from the lower end of the rectifying structure to the molten steel discharge hole is 220 mm, 580 mm, and 600 mm (200 mm ≦ z ≦ 900 mm). In 15-17, it turns out that the drift degree in an immersion nozzle is less than 0.06.

  In addition, Table 4 below shows experimental conditions other than the constituent requirements in the tests 1 to 3 described above.

  Next, in each of the tests 1 to 3 described above, when the degree of drift in the immersion nozzle was less than 0.06, it was evaluated that there was no risk of “◯ (no breakout risk)”. The basis for evaluating “× (with risk of breakout)” when the drift degree is 0.06 or more will be described.

<Causal relationship between coagulation delay and breakout>
The effect produced by using the rectifying structure 10 according to the above-described embodiment is mainly suppression of drift in the mold width direction as described above. By suppressing this drift, the object is to improve the so-called solidification delay and ultimately avoid the so-called breakout (a phenomenon in which molten steel in the solidified shell flows out of the solidified shell). Therefore, here, the degree of coagulation delay for quantitatively evaluating the coagulation delay is defined, and the causal relationship between the degree of coagulation delay and the breakout will be described.

  That is, “solidification delay” refers to partial growth delay of the solidified shell, and the degree of solidification delay is used for quantification. “Degree of coagulation delay” is based on the white band shown in FIG. The “white band” is a linear structure that appears when the solute in front of the shell being solidified is washed by the molten steel flow, and represents the growth of the solidified shell. If there is a difference in the thickness of the shell B at the corner and the shell A at the healthy part, the shrinkage amount due to solidification differs between the solidification delayed part and the healthy part, and tensile stress in the slab width direction concentrates on the solidification delayed part. However, it causes vertical splitting. When the degree of vertical split increases, the molten steel in the solidified shell flows out of the solidified shell and breakout occurs. As shown in FIG. 7, in past data, there is a record that a breakout has occurred when the degree of solidification delay exceeds 40%.

<Quantification method of drift in mold width direction>
Next, a method for quantifying the drift in the mold width direction in actual machine casting will be described. Please refer to FIG. FIG. 8 is an explanatory diagram for explaining a method for quantifying the drift in the mold width direction in actual casting. That is, as shown in this figure, (1) the temperature distribution of the mold in the casting direction is measured using a thermocouple embedded in a vertical line at the center of the mold narrow surface, and (2) the inflection point of the temperature distribution is determined as hot water. (3) The difference Δh between the molten metal level on one side of the mold narrow surface (corresponding to “the right side molten metal surface”) and the molten metal level on the other side (corresponding to “the left side molten metal surface”) is obtained. (4) The drift in the mold width direction was quantified based on the difference Δh.

<Causal relationship between solidification delay and drift in slab width direction>
Next, the causal relationship between the solidification delay and the drift in the slab width direction in actual machine operation will be described with reference to FIG. FIG. 9 is a diagram showing the relationship between the degree of solidification delay and the difference Δh in actual machine operation. According to this figure, when the above difference Δh (corresponding to the “water level difference” in this figure) exceeds 10 [mm], a solidification delay with a solidification delay degree of 40% or more may occur. I understand. Therefore, from the viewpoint of avoiding the breakout described above, the difference Δh [mm] is preferably suppressed to 10 or less.

<Conversion for convenience of verification experiment using water model>
The above-described method for quantifying the drift in the mold width direction utilizes the fact that molten steel is extremely hot, so that the quantification method is used for verification experiments using a water model to be performed instead of the actual machine. Cannot be applied directly. Therefore, a method for quantifying the drift in the mold width direction in a verification experiment using a water model, which has been devised with some contrivance for this quantification method, will be described. Reference is now made to FIG. FIG. 10 is an explanatory diagram for explaining a method for quantifying the drift in the mold width direction in the water model. That is, the above difference Δh [m] can be expressed by the following equation (3).
Δh = ρm × U ₁ ² / (2 × g × (ρm-ρp))-ρm × U ₂ ² / (2 × g × (ρm-ρp)) (3)
However,
ρm [kg / m ³ ]: Density of molten steel ρp [kg / m ³ ]: Density of mold powder
U ₁ [m / s]: Flow velocity of the upward flow of molten steel in the vicinity of one of the mold narrow surfaces
U ₂ [m / s]: Flow velocity of the upward flow of molten steel in the vicinity of the other narrow surface of the mold (U1> U2)
g [m / s ² ]: Gravitational acceleration

For example, if Δh [m] = 0.01, g [m / s ² ] = 9.8, ρm [kg / m ³ ] = 7000, ρp [kg / m ³ ] = 3000 is substituted into the above formula (3), Equation (4) is derived.
U ₁ ² -U ₂ ² = 0.1 ... (4)

<Definition of drift degree, no drift, no drift rate>
By the way, the flow velocity of the molten steel in the narrow mold surface is generally equal to the surface flow velocity of the molten steel in the vicinity of the narrow mold surface (Imamura et al .: Hydraulic study of molten steel flow in continuous casting, iron and steel Vol. 78, No. 3 (1992), p. 439-446), the surface velocity of water at a point 2 cm deep from the surface of the mold 30 cm away from the mold narrow surface as shown in FIG. In the following description, the measured surface flow velocity is regarded as the variables U ₁ and U ₂ . In short, the drift in the mold width direction is evaluated by measuring the surface flow velocity of water.

Then, the “degree of drift in the mold width direction” is defined as in the following formula (5).
(Diffusion degree in mold width direction) = | U ₁ ² -U ₂ ² | / | U ₁ ² -U ₂ ² | cr (5)
However, “| U ₁ ² −U ₂ ² ” cr | is the value of | U ₁ ² −U ₂ ² | when the difference Δh [m] is 0.01 as shown in the above equation (4) (that is, 0.1 ).

  A state where the absolute value of the drift current defined by the above formula (5) is less than 1 is defined as a “no drift current” state.

<Definition of the degree of drift in the immersion nozzle>
As shown in FIG. 11, on the discharge direction axis in the submerged nozzle, the flow rates V ₁ and V ₂ of water on both discharge holes 1 cm inside from the wall surface immediately above the discharge holes were measured using an electromagnetic current meter. Then, the “degree of drift in the immersion nozzle” is defined as the following formula (6).
(Degree of drift in the immersion nozzle) = | V ₁ -V ₂ | / Q _w / S (6)
However,
Q _w : Water flow rate in the immersion nozzle [m ³ / s]
S: Cross-sectional area in the immersion nozzle [m ³ ]

<Boundary conditions for drift in the immersion nozzle>
Next, a causal relationship between “the degree of drift in the immersion nozzle” and “the degree of drift in the mold width direction” will be described with reference to FIG. FIG. 12 is a diagram showing a correlation between “the degree of drift in the immersion nozzle” and “the degree of drift in the mold width direction”. FIG. 12 is a graph showing the correlation between “flow rate in the immersion nozzle” and “flow rate in the mold width direction” by measuring the flow rates U ₁ , U ₂ , V ₁ and V ₂ under the following conditions. . Under the same conditions, when drifting in the mold width direction and when drifting in the mold width direction is suppressed, the flow velocities U ₁ , U ₂ , V ₁ , V ₂ were measured, ”And“ the drift in the mold width direction ”are calculated. From FIG. 12 and Table 5, it is defined that the drift in the mold width direction is suppressed when “the drift degree in the immersion nozzle” is 0.06 or less.

(Test conditions)
Electromagnetic current meter: Manufacturer: Kennek (model number: VM802H)
Mold dimension [mm]: width 1260 x thickness 240
Model type: Water model Molten steel flow rate (or water flow rate) Q _w [cm ³ / s]: Water flow rate 8333
Opening and closing direction of slide plate: mold width direction D [mm]: 85 (see FIG. 13)
θ1 [deg.]: 35 (see FIG. 13)
e [mm]: 100 (see Fig. 13)
f [mm]: 70 (see Fig. 13)
g [mm]: 30 (see Fig. 13)

  As mentioned above, although embodiment of this invention was described based on drawing, it should be thought that a specific structure is not limited to these embodiment and an Example. The scope of the present invention is shown not only by the above description of the embodiments and examples but also by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above embodiment, a three-layer slide plate type flow rate adjustment unit is adopted, but the present invention is not limited to this, and a two-layer type slide plate type flow rate adjustment unit may be adopted.

  Moreover, in the said embodiment, although the two-hole type in which the pair of molten steel discharge holes 7 were formed in the immersion nozzle 2 was demonstrated, the 1-hole type form with which the lower end of the immersion nozzle was open | released is also contained in this invention.

  By using the present invention, it is possible to obtain a rectifying structure capable of suppressing drift due to opening and closing of the slide plate.

2 Immersion nozzle (circular tube)
7 Molten steel discharge hole 10 Rectifying structure 11 Inner tube shape 11a Upper end 11b Lower end 11x Short axis 11y Long axis 20 Flow rate adjustment unit 22 Slide plate (intermediate plate)
x Length of short axis y Length of long axis z Distance from the lower end of the rectifying structure to the upper end of the molten steel discharge hole of the circular pipe part

Claims (1)

In the rectifying structure connected to the downstream side of the slide plate type flow rate adjustment unit used in continuous casting,
The inner tube shape at the upper end is circular, the inner tube shape is continuously deformed from the upper end, and the inner tube shape at the lower end is a flat shape having a major axis and a minor axis,
The short axis of the inner tube shape at the lower end is parallel to the opening and closing direction of the slide plate of the flow rate adjustment unit,
Immediately below the lower end is connected to a circular pipe portion in which the inner pipe shape is a circle having a diameter equal to or larger than the major axis of the inner pipe shape at the lower end and the molten steel discharge hole is drilled.
A rectifying structure satisfying the following formulas (1) and (2):
0.5 ≦ x / y ≦ 0.8 (1)
200 mm ≦ z ≦ 900 mm (2)
However,
x is the length of the short axis of the inner pipe shape at the lower end of the rectifying structure y is the length of the long axis of the inner pipe shape at the lower end of the rectifying structure z is the length of the molten steel discharge hole of the circular pipe portion from the lower end of the rectifying structure Distance to top

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