JP5423434B2 - Continuous casting method and continuous casting apparatus - Google Patents

Description

  The present invention relates to a continuous casting method and a continuous casting apparatus for stably casting a high-quality slab without depending on operating conditions.

  In continuous casting of molten metal such as steel, when molten metal is injected into the mold, the outer peripheral portion of the molten metal in contact with the mold is solidified to form a solidified shell, which is pulled out below the mold. Solidification proceeds in the next cooling zone, and a continuous cast slab is finally formed. The mold is formed of a water-cooled copper plate on the side in contact with the molten metal. A continuous casting apparatus that casts a slab includes a continuous casting mold that is assembled by sandwiching a pair of short side mold plates from both sides in the width direction with a pair of long side mold plates. In this continuous casting mold, the width of the short side mold plate is approximately equal to the thickness of the cast piece to be cast.

  In the process of moving the solidified shell downward while solidification of the solidified shell proceeds in the mold, the solidified shell solidifies and contracts as the solidification progresses. Therefore, the solidified shell that has started to solidify at the meniscus position (molten metal surface position) of the molten metal in the mold contracts when it reaches the lower end of the mold, and the width and thickness of the slab are at the meniscus position during solidification. It becomes smaller than time. In slab continuous casting, since the width is wider than the thickness of the slab, the amount of solidification shrinkage in the slab width direction is large. If there is a gap between the mold and the solidified shell at the bottom of the mold due to the solidification shrinkage of the solidified shell, heat removal from the solidified shell to the mold will be hindered, and sufficient cooling of the mold will not be possible. The lost solidified shell will cause bulging to bulge outward.

  Therefore, a taper is provided at least on the short side of the mold. Providing the taper means that the distance between the lower ends of the mold is reduced with respect to the distance between the opposing short sides with respect to the distance at the meniscus position above the mold.

As shown in FIG. 1 (c), an upper position and a lower position are defined at arbitrary positions in the casting direction, and the distance between both short sides is W ₁ at the upper position and W ₂ at the lower position. Taper amount (%), taper rate (% / m) taper amount (%) = {(W ₁ −W ₂ ) / ΔL} × 100 (3)
Taper rate (% / m) = {(W ₁ −W ₂ ) / W ₀ / ΔL} × 100 (4)
And call it like this. Here, W ₀ may be anywhere as long as it has a fixed length according to a certain width, and can be, for example, a mold upper end width, a mold lower end width, or the like. Here, it is assumed that W ₀ (m) is the meniscus width (W _M ).

  If the short side taper amount is too small, the contact between the solidified shell and the short side mold plate will be uneven, cooling imbalance will occur, the solidified shell growth will be uneven, the slab surface due to molten metal static pressure Cracking occurs. In particular, when the short side taper amount is smaller than an appropriate amount, in the thickness distribution of the solidified shell near the lower end of the mold, as shown in FIG. Are likely to occur, and vertical cracks are likely to occur on the slab surface corresponding to the portion 12. When the short side taper amount is too large, the contact between the solidified shell 10 and the short side mold plate becomes strong, and an excessive stress (friction restraining force) is applied to the solidified shell, and the solidified shell 10 breaks and the shell breaks. A breakout occurs. Alternatively, the mold life may be reduced due to an increase in the frictional restraining force between the solidified shell 10 and the mold.

  Regarding an appropriate short side taper, for example, Patent Document 1 discloses that the short side taper ratio βn is set to 0.7 to 1.3% / m.

  As shown in FIG. 1C, the surface facing the solidified shell 10 of the conventional short-side mold plate 2 ′ (hereinafter also referred to as “tapered surface 6”) is a single flat surface from the top to the bottom. It is processed as follows. However, the solidification shrinkage rate of the solidification shell 10 is not constant at each position in the casting direction in the mold, and the solidification shrinkage rate is fast near the meniscus, and the solidification shrinkage rate becomes slower as it approaches the lower end of the mold. Therefore, it is considered that the surface of the solidified shell 10 in contact with the short side mold plate 2 ′ is not a flat surface but forms a curved surface in which the taper amount of the solidified shell 10 decreases as it goes below the mold.

  Patent Document 2 discloses a taper control method for controlling the taper of the mold short side as a curved surface. The short side mold is supported at at least three points on the back surface and deformed. A pressure device is attached to at least one of the three points, for example, the central portion, and the surface of the short side copper plate and the free contraction profile are matched in advance and during operation, so that more uniform heat removal is possible. By applying a force of 2 to 5 tons to the central load point, the maximum amount of deflection becomes 0.33 to 0.83 mm, which is considered to be a sufficient amount in view of the solidification shrinkage of the molten steel.

In Patent Document 3, the optimum short side taper is obtained by theoretical analysis. The optimum short side taper depends on the distance Z along the casting direction from the meniscus and the casting speed V, and the optimum taper rate (% / ^M ) is proportional to Z ^−1/2 and proportional to (4-V) (m / min). According to Example 1 and FIG. 2 of the same document, the short side of the mold having a cross-sectional dimension of 20.8 cm × 105 cm is formed into a shape having a three-step taper, and the taper rate is 2% / m, 0.7% / m, 0.4% / m. Further, according to Example 2 and FIG. 3, the short side of the mold having a cross-sectional dimension of 22 cm × 124 cm is formed into a shape having a three-step taper, and the taper rate is 4% / m, 1.3% / m,. 8% / m. In this way, a mold having two or three or more tapers in the casting direction is called a “multi-stage taper mold”, and a short-side mold plate having such a taper is called a “multi-stage taper short-side mold plate”. (See FIG. 1 (a) and FIG. 1 (b)). For example, the two-stage tapered short sides mold plate 2 shown in FIG. 1 (a), the taper ratio of the tapered surface 6 _U and 6 _L is changed in a tapered changing point P.

  By the way, in continuous casting, the productivity of slab can be improved, so that casting speed is high. Also in continuous casting of slabs, the casting speed has increased from around 2.0 m / min to about 3.0 m / min recently. In continuous casting using the multistage tapered short side mold plate 2, the optimum shape of the multistage tapered short side mold plate 2 changes as the casting speed increases, and the casting method using the multistage tapered short side mold plate 2 also changes. . Patent Document 4 discloses that when the casting speed is increased, the degree of bending of the multi-stage tapered short side mold plate is relaxed and the overall inclination is reduced.

  In continuous casting of slabs, cast slabs have various widths for each destination, so that the cast slab width is changed while continuous casting is continued. For example, as shown in FIG. 3, in the continuous casting mold 1, a short-side drive mechanism 4 for horizontally moving a multi-stage tapered short-side mold plate 2 (hereinafter also referred to as “short-side mold plate 2”) in the long-side direction. The slab width can be changed during casting by changing the position of the short side mold plate 2 while the short side mold plate 2 is sandwiched between the long side mold plates 3. That is, cast pieces having various widths can be cast using the same continuous casting mold 1 without exchanging both the long side mold plate 3 and the short side mold plate 2.

  Patent Documents 5 and 6 describe methods for estimating the solidification behavior of a slab in a mold by calculation. When the inclination of the casting direction of the mold or the casting speed is set to an arbitrary value, the thickness of the solidified shell at each part around the mold is calculated. Based on this result, the ratio between the maximum value and the minimum value of the solidified shell thickness at the lower end of the mold, the binding force between the solidified shell and the mold, and the gap amount can be obtained. Further, Patent Document 7 describes that the short side mold surface of the mold is formed in a curved surface gradient or a multistage gradient shape along the solidification shrinkage amount profile of the short side corner portion of the slab.

  Further, Patent Document 8 always uses a mold part having an inner peripheral length that is approximately equal to the contraction outline of the initial solidified shell by displacing the meniscus position of the molten steel up and down, and the contact state between the mold and the solidified shell. Is disclosed in order to keep it optimal. Further, in Patent Document 8, as a physical quantity indicating a contact state between the mold copper plate and the solidified shell, a combination of a pull-out resistance value in the mold, a copper plate temperature, and a temperature difference between the water supply side and the water discharge side of the mold cooling water is used. Based on the above, it is disclosed that the meniscus position is displaced up and down.

  Furthermore, Patent Document 9 discloses a mold in which the long side taper of the mold is a two-stage taper and the taper change point is 80 to 300 mm from the meniscus position for the purpose of promoting powder inflow.

Japanese Patent Laid-Open No. 2005-21936 JP-A-2-247059 JP-A-56-53849 Japanese Patent Laid-Open No. 3-210953 JP 2006-346735 A JP 2006-346736 A JP-A-57-79047 JP-A-6-297101 JP 2003-305540 A

  By the way, when performing continuous casting using a multistage taper mold, in order to stably cast high quality slabs without surface cracks and internal cracks, the solidification uniformity of the solidified shell in the multistage taper mold is as much as possible. It is required to increase the frictional restraining force between the solidified shell and the multistage tapered short side mold plate as much as possible.

  On the other hand, in the continuous casting operation, in addition to the above-described slab width, there are many cases where it is desired to change other operating conditions such as casting speed from the viewpoint of improving productivity. Some of these operating conditions affect both the solidification uniformity and frictional restraint force of the solidified shell. For example, increasing the casting speed is desirable because the solidification uniformity increases, but it is not desirable because the frictional restraint force also increases. On the other hand, lowering the casting speed is desirable because the frictional restraining force is decreased, but it is not desirable because the solidification uniformity is also decreased. If the operating conditions such as the casting speed are changed in this way, the solidification uniformity and the frictional restraining force have a conflicting relationship in casting a high-quality slab, so the operating conditions are easily changed during operation. It is not possible.

  In addition, as described above, the optimum shape of the multi-stage tapered short side mold plate changes depending on the operating conditions such as the casting speed, but in order to cope with changes in the operating conditions, multiple types of molds are prepared for each operating condition. Therefore, it is not practical from the viewpoint of cost and production efficiency.

  Furthermore, as described in Patent Document 7, even if an attempt is made to form the short side mold surface of the mold into a shape along the solidification shrinkage profile of the short side corner portion of the slab, the specific position of the change point of the multistage taper It is very difficult to set the value appropriately.

  Further, in the method of changing the meniscus position in the mold as in Patent Document 8, the workability of the change work is poor, and when the meniscus position is raised, operation troubles such as molten metal overflowing from the mold occur. The potential increases. For this reason, during the continuous casting operation, it is preferable to keep the meniscus position in the mold constant.

  The technique of Patent Document 9 defines the change point position of the long side taper in relation to the powder inflow, and the dependency of the change point position of the short side mold plate taper on the operating conditions such as the casting speed. There is no disclosure about.

  As described above, conventionally, in continuous casting using a multi-stage taper mold, while satisfying the constraints of both the solidification uniformity and the frictional constraint force, which are in the above-mentioned conflicting relationship, without using multiple types of molds for replacement. There was no technology that could cope with changes in operating conditions such as casting speed. Therefore, such a technique has been strongly demanded.

  Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to operate a continuous casting while satisfying both the restrictions of solidification uniformity and frictional restraining force which are in a contradictory relationship. It is an object of the present invention to provide a new and improved continuous casting method and continuous casting apparatus that can cope with changes in conditions.

In order to solve the above problems, according to one aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more tapers different from each other in the casting direction, and the multi-stage tapered short side mold plates from both sides in the width direction are provided. In a continuous casting method using a mold composed of a pair of long-side mold plates sandwiched, the solidification average of a solidified shell of molten metal in the mold is obtained by moving the multi-stage tapered short-side mold plate in the casting direction during casting. The position of the taper change point of the multistage tapered short side mold plate is set in the mold so that both the frictional restraining force between the solidified shell and the multistage tapered short side mold plate is maintained substantially constant once . There is provided a continuous casting method characterized by moving relative to a meniscus position of a molten metal in a casting direction.

In order to solve the above problem, according to another aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate having a width A mold composed of a pair of long side mold plates sandwiched from both sides in the direction, and by moving the multi-stage tapered short side mold plate in the casting direction during casting , the solidification uniformity of the solidified shell of the molten metal in the mold, and The position of the taper change point of the multi-stage tapered short side mold plate is set so that both the frictional restraining force between the solidified shell and the multi-stage tapered short side mold plate are maintained substantially constant . There is provided a continuous casting apparatus comprising: a short side drive mechanism that moves relative to a meniscus position in a casting direction.

  Further, the multi-stage tapered short side mold plate may be moved in the casting direction during casting according to the operating conditions of continuous casting.

  Furthermore, the operation conditions of the continuous casting may affect both the solidification uniformity of the solidified shell solidified by the molten metal and the frictional restraining force between the solidified shell and the multi-stage tapered short side mold plate. You may make it the conditions.

  The continuous casting operation condition may include a casting speed, and the multi-stage tapered short side mold plate may be moved in the casting direction during casting according to the casting speed.

  Further, the multi-stage tapered short side mold plate is moved upward in the casting direction during casting according to the increase in the casting speed, and the multi-stage tapered short side mold plate is moved downward in the casting direction during casting according to the decrease in the casting speed. You may make it move to.

Further, the continuous casting operation condition includes a carbon concentration of the molten metal,
The multi-stage tapered short side mold plate may be moved in the casting direction during casting according to the carbon concentration of the molten metal.

  The operation conditions of the continuous casting include the surface average heat removal flux of the multistage tapered short side mold plate, and the multistage taper short side mold plate is moved in the casting direction during casting according to the surface average heat removal flux. You may make it make it.

Further, the multi-stage taper short side mold plate is moved upward in the casting direction during casting according to the increase in the surface average heat extraction flux, and the multi-stage taper short side during casting according to the decrease in the surface average heat extraction flux. The mold plate may be moved downward in the casting direction.
In order to solve the above problem, according to another aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate having a width In a continuous casting method using a mold composed of a pair of long side mold plates sandwiched from both sides in the direction, the multi-stage taper short side plate is moved in the casting direction during casting according to the casting speed, thereby The position of the taper change point of the side mold plate is moved relative to the meniscus position of the molten metal in the mold in the casting direction, and the distance from the meniscus position to the taper change point of the multistage taper short side mold plate is represented by x ( mm), and when the casting speed is V (m / min), the casting speed is decreased from V ₀ to V from the state of continuous casting at the casting speed V ₀ and the change point position x _0. Is When the following formula (1) is satisfied and the casting speed is increased from V ₀ to V, the multi-stage tapered short side mold plate is moved in the casting direction during casting so as to satisfy the following formula (2). A continuous casting method is provided.
x ₀ <x ≦ −200 (V−V ₀ ) + x ₀ : V <V ₀ (1)
x ₀ > x ≧ −200 (V−V ₀ ) + x ₀ : V> V ₀ (2)
In order to solve the above problem, according to another aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate having a width A taper change of the multi-stage tapered short side mold plate by moving the multi-stage tapered short side mold plate in the casting direction during casting according to the casting speed, and a mold composed of a pair of long side mold plates sandwiched from both sides in the direction. A short-side drive mechanism for moving the position of the point relative to the meniscus position of the molten metal in the mold in the casting direction, and the distance from the meniscus position to the taper change point of the multistage tapered short-side mold plate x (mm) and when the casting speed is V (m / min), the casting speed is decreased from V ₀ to V from the state of continuous casting at the casting speed V ₀ and the change point position x _0. If you want to When the above formula (1) is satisfied and the casting speed is increased from V ₀ to V, the multi-stage tapered short side mold plate is moved in the casting direction during casting so as to satisfy the following formula (2). A continuous casting apparatus is provided.
x ₀ <x ≦ −200 (V−V ₀ ) + x ₀ : V <V ₀ (1)
x ₀ > x ≧ −200 (V−V ₀ ) + x ₀ : V> V ₀ (2)
In order to solve the above problem, according to another aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate having a width In a continuous casting method using a mold composed of a pair of long side mold plates sandwiched from both sides in the direction, by moving the multistage tapered short side mold plate in the casting direction during casting according to the carbon concentration of the molten metal, The position of the taper change point of the multi-stage taper short side mold plate is moved relative to the meniscus position of the molten metal in the mold in the casting direction, and the carbon concentration C (mass%) of the molten metal is 0.05 <C <. The continuous casting is characterized in that when 0.2, the multi-stage tapered short side mold plate is moved downward in the casting direction during casting than when C ≦ 0.05 or C ≧ 0.2. A method is provided.
In order to solve the above problem, according to another aspect of the present invention, a pair of multi-stage tapered short side mold plates having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate having a width A mold composed of a pair of long-side mold plates sandwiched from both sides in the direction, and the multi-stage tapered short-side mold plate by moving the multi-stage tapered short-side mold plate in the casting direction during casting according to the carbon concentration of the molten metal. A short-side drive mechanism for moving the position of the taper change point relative to the meniscus position of the molten metal in the mold in the casting direction, and the carbon concentration C (mass%) of the molten metal is 0.05 < When C <0.2, the multi-stage taper short side mold plate is moved downward in the casting direction during casting than when C ≦ 0.05 or C ≧ 0.2. A continuous casting apparatus is provided.

  In the above configuration, the position of the taper change point of the multistage tapered short side mold plate is moved relative to the meniscus position of the molten metal in the mold by moving the multistage tapered short side mold plate in the casting direction during casting. . Thereby, the position of the taper change point of the multi-stage tapered short side mold plate can be moved in the vertical direction while keeping the meniscus position in the mold as the fixed position, and can be moved closer to or away from the meniscus position. Therefore, by adjusting the position of the taper change point of the multi-stage taper short side mold plate during casting according to changes in operating conditions such as casting speed, solidification uniformity in a reciprocal relationship before and after the change of operating conditions And the frictional restraining force can be controlled to be substantially constant. Therefore, it is possible to cope with a change in operating conditions such as casting speed while satisfying both the solidification uniformity and the frictional restraining force, which are in a reciprocal relationship.

  As described above, according to the present invention, it is possible to cope with a change in operating conditions of continuous casting while satisfying both the solidification uniformity and the frictional restraining force which are in a contradictory relationship. Therefore, even if operating conditions such as casting speed are changed, a high quality slab having no surface cracks and internal cracks can be stably cast.

It is a figure explaining the taper surface of a general multistage taper short side mold plate, (a) is a 2 step taper short side mold plate, (b) is a 3 step taper short side mold plate, (c) is a 1 step taper. It is a figure which shows a short side mold plate. It is a cross-sectional view which shows the shape of the solidification shell in the casting_mold | template lower end calculated | required with the calculation method which concerns on one Embodiment of this invention. It is a figure which shows the basic composition of the continuous casting mold which concerns on the embodiment, (a) is a top view, (b) is a partial cross section front view. It is a figure which shows the change of the solidification uniformity and frictional restraint force when changing the up-and-down taper ratio and the casting speed in the slab width of 1100 mm. It is a figure which shows the change of the solidification uniformity and frictional restraint force when changing the up-and-down taper ratio and the casting speed in the slab width of 2200 mm. It is a figure which shows the change of the solidification uniformity and the frictional restraint force when changing the change point position x and the casting speed in the slab width of 1100 mm. It is a figure which shows the change of the solidification uniformity and friction restraint force when changing the change point position x and casting speed in slab width 2200mm. It is a figure which shows the change of the coagulation | solidification uniformity when changing a total taper rate, and a frictional restraint force. It is a figure which shows the change of the solidification uniformity and the frictional restraint force when changing the change point position x and the casting speed V at a slab width of 1100 mm, a vertical taper ratio of 4.0, and a total taper ratio of 1.6% / m. . In the continuous casting method which concerns on the embodiment, it is a figure which shows the suitable range of the change point position x when changing the casting speed V from 1.5 m / min. Changes in solidification uniformity and frictional restraint force when changing the change point position x and carbon concentration C of the molten metal at a slab width of 1100 mm, a vertical taper ratio of 4.0, and a total taper ratio of 1.6% / m. FIG. It is a figure which shows the relationship between the solidification uniformity and carbon concentration C when change point position x is 200 mm. Solidification when changing the change point position x and the surface average heat removal flux q at a slab width of 1100 mm, a vertical taper ratio of 4.0, a total taper ratio of 1.6% / m, and a casting speed V = 1.5 m / min. It is a figure which shows the change of a uniformity and a frictional restraint force. It is a figure which shows the structure of the continuous casting apparatus which concerns on the same embodiment. It is a figure which shows the structure of the control apparatus of the continuous casting apparatus which concerns on the same embodiment. It is a figure which shows the structure of the continuous casting apparatus which concerns on the example of a change of the embodiment.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

Below, the continuous casting method and continuous casting apparatus which concern on one Embodiment of this invention are demonstrated in detail. The description will be made in the following order.
1. Definition of terms 2. Outline of continuous casting method 3. Relationship between casting speed and change point position 4. Continuous casting method according to casting speed 5. Continuous casting method according to the carbon concentration of the molten metal 6. Configuration of continuous casting machine effect

[1. Definition of terms]
First, terms used in this specification are defined.

The meniscus position is the height position of the meniscus (molten metal surface) of molten metal (for example, molten steel) in the mold.
The casting direction is a direction in which the slab is pulled out from the mold, and is, for example, a vertical direction (up and down direction).
The multi-stage tapered short side mold plate is a short side mold plate having two or more tapers different in the casting direction. The two-step tapered short side mold plate is a short side mold plate having two tapers different in the casting direction (see FIG. 1A), and the three-step tapered short side mold plate is different in the casting direction. It is a short side mold plate having three tapers (see FIG. 1A).
The taper changing point P is a portion where the taper changes in the multi-stage tapered short side mold plate. In the case of the two-step taper short side mold plate 2 shown in FIG. 1A, the taper change point P is one point, and in the case of the three-step or more taper short side mold plate shown in FIG. The change points P _U and P _L are two or more points.
The change point position x (mm) is the distance from the meniscus position to the first taper change point P of the multistage tapered short side mold plate (that is, the relative height between the meniscus position and the taper change point). In the two-step taper short side mold plate shown in FIG. 1A, the change point position x is the distance from the meniscus position 11 to the taper change point P. In the three-step taper short side mold plate shown in FIG. , change point position x is the distance from the meniscus position 11 to the upper tapered changing point P _U. The maximum casting speed in continuous casting is V _M (m / min), and the casting speed is V (m / min).

The solidification uniformity is a parameter representing the uniformity of the solidified state of the solidified shell formed by solidification of the molten metal in the mold 1. For example, as shown in FIG. 2, the ratio B / A between the maximum value A and the minimum value B on the long side of the solidified shell 10 can be defined as the solidification uniformity (dimensionalless amount).
The frictional restraining force is a parameter representing the magnitude of the restraining force generated by the friction between the mold and the solidified shell during continuous casting. For example, a value obtained by normalizing the frictional restraint force at each width of the mold obtained by calculation described later with a reference value at each width (frictional restraint force when the taper rate is 1.0% / m with a one-step taper) It can be used as a frictional restraint force (dimensionalless amount).
The carbon concentration of the molten steel metal is the concentration (% by mass) of carbon in the molten metal (for example, molten steel).
“Casting” means a state in which a mold is installed in a continuous casting apparatus and molten metal can be injected into the mold. For example, the period from when the mold is installed by assembling the pair of short side mold plates and the pair of long side mold plates to when the short side mold plate and the long side mold plate are disassembled is `` under casting '' include. Therefore, “during casting” means not only the actual casting period in which the molten metal is injected into the mold and the slab is cast, but also the period in which the molten metal is not injected into the mold before the actual casting period. In addition, a period in which molten metal is not injected into the mold after the actual casting period is included. On the other hand, after disassembling the mold in the continuous casting device, the period from when the short side mold plate and the long side mold plate are reassembled and the mold is reinstalled cannot be poured into the mold. Not included.

Further, the total taper rate T _T , the upper taper rate T _U , the lower taper rate T _L , and the vertical taper ratio are defined as follows.

As shown in FIGS. 1 (a) and 1 (b), the distance between both short sides is W _M (m) at the meniscus position, W _B (m) at the lower end of the mold, and the distance from the meniscus position to the lower end of the mold is L. When (m) is set, the total taper rate T _T (% / m) is set to T _T (% / m) = {(W _M −W _B ) / W _M / L} × 100 (5)
It is defined as

In the taper surface 6 _U on the casting direction at the top of the multistage tapered short side mold plate 2, optionally define the upper and lower positions, the distance between both short sides, W _{1 (m)} at the upper position, the lower position When W ₂ (m) and the distance from the upper position to the lower position are set to ΔL (m) (FIGS. 1A and 1B), the upper taper ratio T _U (% / m) is set to T _U (% / m). ) = {(W ₁ −W ₂ ) / W _M / ΔL} × 100 (6)
It is defined as

As shown in FIG. 1 (a) and (b), the lower tapered surface 6 _L of the casting direction lowermost multistage tapered short side mold plate 2, optionally define the upper and lower positions, the distance between both short sides the, _W 3 (m) at the upper position, _W 4 (m) in the lower position, and the distance from the upper position to the lower position spaced a [Delta] L (m), the lower tapered rate _T L a (% / m) T _L (% / _M ) = {(W ₃ −W ₄ ) / W _M / ΔL} × 100 (7)
It is defined as

Vertical taper ratio is
Vertical taper ratio = upper taper rate / lower tapered index _{= T U / T L (8} )
It is defined as

[2. Outline of continuous casting method]
In the continuous casting method according to the present embodiment, as in FIG. 3, a pair of multi-stage tapered short side mold plates 2 having two or more different tapers in the casting direction, and the multi-stage tapered short side mold plate 2 from both sides in the width direction. This is a continuous casting method using a continuous casting mold 1 composed of a pair of long side mold plates 3 sandwiched therebetween. In the continuous casting method according to the present embodiment, the meniscus position 11 of the molten metal in the mold 1 is moved by moving the multi-taper short side mold plate 2 up and down in the casting direction during casting according to the operating conditions of continuous casting. On the other hand, the taper change point P (change point position x) of the multistage tapered short side mold plate 2 is relatively moved in the casting direction.

  This operating condition affects both the solidification uniformity of the solidified shell formed by solidification of the molten metal in the mold 1 and the frictional restraining force between the solidified shell and the short side mold plate 2. For example, the casting speed, the type of molten metal (for example, steel type), the surface average heat removal flux of the short side mold plate 2 and the like. The kind of molten metal is, for example, the carbon concentration C of the molten metal.

  In accordance with such operating conditions, the taper change point P of the multi-stage tapered short side mold plate 2 relative to the meniscus position 11 is moved relative to the casting direction by moving the multi-stage tapered short side mold plate 2 up and down in the casting direction during casting. By moving, the change point position x can be adjusted to a position suitable for the operating conditions. For example, the taper changing point P is brought closer to the meniscus position 11 and the changing point position x is reduced by moving the short side mold plate 2 upward in the casting direction during casting according to an increase in casting speed. On the other hand, the taper changing point P is moved away from the meniscus position 11 and the changing point position x is increased by moving the short side mold plate 2 downward in the casting direction during casting in accordance with the decrease in casting speed.

  As a result, the changing point position x of the multi-stage tapered short side mold plate 2 can be controlled to an appropriate position during casting according to the operating conditions, so that the solidification uniformity and frictional constraints that are in a reciprocal relationship before and after the operating conditions are changed. The force can be maintained at a substantially constant value. Therefore, it is possible to cope with a change in operating conditions for continuous casting while satisfying both the solidification uniformity and the frictional restraint. Therefore, even if the operating conditions such as the casting speed are changed, a high-quality slab having no surface cracks and internal cracks can be stably cast.

  As described above, in the continuous casting method according to the present embodiment, the multi-step tapered short side mold plate 2 is moved up and down in the casting direction during casting according to the operating conditions, and the changing point position x is changed with respect to the meniscus position 11. It is characterized by that.

[3. Relationship between casting speed and change point position]
Here, prior to detailed description of the continuous casting method according to the present embodiment, first, the relationship between the casting speed and the change point position x, which is the basis of the continuous casting method, will be described in detail.

  Patent Documents 5 and 6 describe a method for estimating the solidification behavior of a slab in a mold by calculation. When the inclination of the casting direction of the mold or the casting speed is set to an arbitrary value, the thickness of the solidified shell 10 at each part around the four sides of the mold is calculated as shown in FIG. Based on this result, the ratio B / A between the maximum value A and the minimum value B of the solidified shell thickness at the lower end of the mold, the frictional restraint force between the solidified shell and the mold, and the gap amount can be obtained.

  Using the calculation methods described in Patent Documents 5 and 6, the shape of the solidified shell 10 at the lower end of the mold and the frictional restraining force between the solidified shell 10 and the mold were determined for continuous casting using a multistage tapered short side mold plate. The shape of the solidified shell 10 at the lower end of the mold is derived as shown in FIG. 2 by calculation. A portion with a thin solidified shell thickness may be formed on the long side of the solidified shell 10 in the vicinity of the slab corner, and the solidified shell thickness at this portion is defined as the minimum value B of the shell thickness. In this embodiment, the ratio B / A between the maximum value A and the minimum value B of the solidified shell thickness is referred to as “solidification uniformity”. When casting with good solidification uniformity is performed, the shell thickness B of the portion with the small shell thickness on the long side near the corner approaches the shell thickness A of the other thick portion.

  Actually casting the molten steel, adding S to the molten steel in the mold during casting, and evaluating the thickness distribution of the solidified shell at the lower end position of the mold by sulfur printing of the slab after solidification. It was found that the uniformity was in good agreement with the maximum and minimum ratios of the mold bottom solidified shell thickness obtained from sulfur printing. Therefore, it is possible to find a suitable continuous casting method using the solidification uniformity obtained by calculation as an index.

  If the value of solidification uniformity (B / A) obtained by calculation is 0.7 or more, good solidification uniformity can be ensured even in actual casting. If the solidification uniformity (B / A) value is less than 0.7, the solidified shell may break and break out. Further, if the frictional restraint force obtained by calculation (reference value at each width (value normalized by the frictional restraint force when the taper rate is 1.0% / m with a one-step taper)) is 2.0 or less Even in actual casting, good casting with less restraint can be performed. Further, by setting the solidification uniformity (B / A) and the frictional restraining force within the above preferred ranges, it has been confirmed from the results of actual continuous casting that breakout does not occur when continuous casting is performed.

  Hereinafter, the solidification uniformity and the frictional restraint force are calculated by a calculation method based on the above-mentioned Patent Documents 5 and 6 (hereinafter also referred to as “calculation method according to the present embodiment”), and the optimum of the multistage tapered short side mold plate is calculated. We will consider the shape.

In a conventional multi-stage tapered short side mold plate, particularly a two-step tapered short side mold plate, the distance L from the meniscus position to the lower end of the mold is about 900 mm, and the change point position x is about 300 mm. When the maximum casting speed V _M to adopt casting speed of up to about 2.5 m / min, adopts 4.0 degree taper as a vertical taper ratio, good castability both coagulation uniformity and frictional binding Was able to be realized. This point can be confirmed by the calculation method according to the present embodiment.

  The slab width W is 1100 mm (narrow width), the total taper rate is 1.6% / m, the changing point position x of the two-step taper short side mold plate is constant 300 mm, and the casting speed is 1.0 to 3.0 m / m. The bending state of the short side mold plate was changed by changing the min and changing the upper and lower taper ratio of the two-step taper short side mold plate, and the solidification uniformity and frictional restraint force were calculated by the calculation method according to this embodiment. .

  As shown in FIG. 4, the same vertical taper ratio improves the solidification uniformity as the casting speed increases, but also increases the frictional restraint force. It can be seen that in order to keep both the solidification uniformity and the frictional restraining force within a good range, it is preferable to lower the vertical taper ratio as the casting speed increases. When the upper and lower taper ratio range in which both the solidification uniformity and the frictional restraining force can be satisfactorily maintained are examined for each casting speed, the preferable range of the upper and lower taper ratio is 5.0 or less at a casting speed of 2.0 m / min. However, at 2.5 m / min, the preferred range of the vertical taper ratio was 4.0 or less, and at the casting speed of 3.0 m / min, the preferred range of the vertical taper ratio was 3.0 or less.

  Next, the shape of the short side mold plate having a good slab width W = 1100 mm and good solidification uniformity and frictional restraint force (with an up / down taper ratio of 3.0 optimized for a casting speed of 3.0 m / min) The slab width W was as wide as 2200 mm. When the slab width W was changed, the total taper rate was maintained at 1.6% / m. As a result, the slab width W = 2200 mm and the vertical taper ratio was 1.7.

  As shown in FIG. 5, when the solidification uniformity and the frictional restraint force are calculated by the calculation method according to the present embodiment for the slab width W = 2200 mm (wide), the slab width is maintained while keeping the total taper rate constant. When W was widened, it was found that when the casting speed was 3.0 m / min, the preferred range of the upper and lower taper ratio decreased to less than 1.7, and the solidification uniformity also decreased. That is, it was found that, in a mold optimized for high speed casting up to a casting speed of 3.0 m / min at a slab width W = 1100 mm, if the slab width W is 2200 mm wide, it is out of the optimum range.

  Therefore, when the slab width W is 1100 mm, when optimizing the multi-step taper for each casting speed, the vertical taper ratio is kept constant at 4.0 instead of fixing the change point position x and changing the vertical taper ratio. Then, the change point position x was changed. The total taper rate was set to 1.6% / m, the change point position x was changed, and the solidification uniformity and the frictional restraint force were calculated by the calculation method according to this embodiment. The result is shown in FIG. Based on the upper limit threshold 2.0 of the frictional restraint force, the preferred range of the change point position x is 300 mm or less at a casting speed of 2.5 m / min or less, and the preferred change point position x at a casting speed of 3.0 m / min. The range became 200 mm or less.

  Next, a short side mold plate having a change point position x suitable for a slab width W = 1100 mm (a mold shape having a change point position of 200 mm optimized up to a casting speed of 3.0 m / min) is used. The calculation was performed for casting with a slab width W = 2200 mm. When the total taper rate was maintained at 1.6% / m and the slab width W was increased while the total taper rate was constant, the vertical taper ratio was 2.5 at the slab width W = 2200 mm. Therefore, in the case of the slab width W = 2200 mm, the total taper rate is 1.6% / m, the vertical taper ratio is kept constant at 2.5 as described above, and the change point position x is changed. FIG. 7 shows the result of calculating the solidification uniformity and the frictional restraint force by the calculation method according to the embodiment. As is apparent from FIG. 7, it was found that if the change point position x is 200 mm or less, a good range can be secured at a casting speed of 3.0 m / min or less even if the slab width W = 2200 mm. Accordingly, when casting at a maximum casting speed of 3.0 m / min, continuous casting can be performed satisfactorily if the displacement point position is 200 mm or less.

  Similarly, at a casting speed of 3.75 m / min, if the change point position x is 50 mm or less, good casting is performed regardless of whether the slab width W is 1200 mm (FIG. 6) or 2200 mm (FIG. 7). be able to. Therefore, when casting at a maximum casting speed of 3.75 m / min, if the displacement point position is 50 mm or less, continuous casting can be performed satisfactorily.

  As described above, it is optimal to change the change point position x when compared with a suitable upper limit taper ratio when applied to a wide width using a mold optimized by changing the vertical taper ratio at the time of narrow width for each casting speed. When a wide mold is used, the preferred vertical taper ratio can be increased, and when the change point position x is changed, the vertical taper is more suitable at the wide width than at the narrow width. Although the ratio decreased, it was found that the solidification uniformity increased conversely.

  That is, when determining the optimum taper shape of the multi-stage tapered short side mold plate when the casting speed becomes high, as shown in FIGS. 6 and 7, the change point position x is raised upward as the casting speed becomes higher. Thus, it was found that better solidification uniformity and frictional restraint force can be maintained even when the slab width W is wider than when the vertical taper ratio is changed.

  By the way, the relationship between FIG. 6 and FIG. 7 is confirmed by calculation and actual machine tests to show the same relationship in the range of 600 mm to 2500 mm, which is a slab width W assumed from an industrial viewpoint. .

From the relationship of FIG. 6 and FIG. 7, the solidification uniformity is 0.7 or more, expressed in equation conditions frictional restraining force is preferably a range of 2.0 or less as a variable of maximum casting speed V _M, the following It is derived as shown in equations (9) and (10).
50 ≦ x ≦ 300: V _M ≦ 2.5 (9)
50 ≦ x ≦ 300−200 (V _M −2.5): 2.5 <V _M ≦ 3.75 (10)

The reason why the lower limit of x is set to 50 mm is that if the change point position x is above the mold, the effect of the multi-step taper cannot be obtained sufficiently, and the normal one-step taper is hardly affected. From equation (10), _{V M} is a solution eliminates exceeds 3.75 m / min. That is, the upper limit of _{V M} in the present embodiment is 3.75 m / min. In addition, the upper limit of x is set to 300 mm because when the upper and lower taper ratio is to be secured above a certain value, if the upper strong taper region becomes longer, the taper rate of the lower taper portion becomes smaller and the total taper rate is constant. When casting with a narrow width by changing the half width W, the lower taper rate becomes extremely small and tends to become reverse taper (wider as the taper goes down), and the slab bulges easily under the mold. Because it becomes.

Control of the change point position x according to the present embodiment as described above, the effect is remarkable as the maximum casting speed V _M is increased. Maximum casting speed _{V M} can exhibit particularly remarkable effects in the high-speed casting of 2.5 m / min greater.

  Next, using the same two-step tapered short side mold plate as above (mold having a change point of 200 mm), the casting speed is fixed at 1.5 m / min and the slab width W is fixed at 1100 mm, and the total taper ratio is changed. Solidification uniformity and frictional restraint force were calculated. The slab thickness was 240 mm. The results are shown in FIG. As is apparent from FIG. 8, when the total taper rate is 0.5% / m or more, the solidification uniformity can be maintained at a good value (0.7 or more). Further, if the total taper rate is 2.0% / m or less, the frictional restraining force is small (2.0 or less) and can be held well.

  As the multi-stage tapered short side mold plate according to the present embodiment, a mold plate having a taper of three or more stages may be used, but as a result of setting the change point position x upward, The effect can be fully exhibited.

  In the present embodiment, the cast slab thickness is preferably 220 mm to 300 mm, more preferably 240 mm to 300 mm. When the slab thickness exceeds 300 mm, excessive equipment is required as a continuous casting mold for changing the slab width W during casting, which is substantially difficult to realize. If the casting thickness is less than 240 mm, the diameter of the immersion nozzle for injecting the molten metal from the tundish must be reduced, so that uniform injection of the molten metal becomes difficult. When the casting thickness is less than 220 mm, more uniform injection becomes more difficult.

  According to the above description, since the optimum taper shape of the short side mold plate 2 changes according to the casting speed, in order to cope with the change in the operating conditions such as the casting speed, It can be seen that the position (change point position x) of the taper change point P of the side mold plate 2 may be positioned at the optimum height position in the casting direction. However, conventionally, there is no known continuous casting apparatus provided with a short side drive mechanism that moves the changing point position x in the casting direction with respect to the meniscus position 11 by moving the short side mold plate 2 up and down.

  Therefore, as will be described in detail below, the continuous casting method according to this embodiment uses a novel short-side drive mechanism to move the short-side mold plate 2 up and down in the casting direction during casting according to changes in operating conditions. By moving, the changing point position x of the short side mold plate 2 with respect to the meniscus position 11 is positioned at the optimum height position suitable for the changed operating conditions, and high quality slabs are stably cast. It is something to try.

[4. Continuous casting method according to casting speed]
Next, with reference to FIG. 9, the continuous casting method of moving the short side mold plate 2 up and down during casting according to the casting speed according to the present embodiment will be described in detail. FIG. 9 shows solidification uniformity and frictional restraint force when changing the change point position x and the casting speed V at a slab width W = 1100 mm, a vertical taper ratio of 4.0, and a total taper ratio of 1.6% / m. It is a figure which shows a change. The data in FIG. 9 corresponds to the data in FIG.

  As shown in FIG. 9, the frictional restraint force and the solidification uniformity change according to the casting speed V. Therefore, it can be seen that the casting speed V is an operating condition that affects both the frictional restraining force and the solidification uniformity of the solidified shell 10 (see FIG. 2) in continuous casting. Moreover, the casting speed V is an operating condition that has an adverse effect on the frictional restraining force and the solidification uniformity from the viewpoint of stably casting a high-quality slab.

  That is, for example, as shown by the wavy ellipse in FIG. 9, when the casting speed V is increased when operating at a changing point position x fixed at, for example, 200 mm, the solidification uniformity increases, but the frictional restraining force also increases. Since it increases, it is not desirable from the viewpoint of stably casting a high-quality slab. On the other hand, if the casting speed V is reduced under the same conditions, the frictional restraining force is lowered, but the solidification uniformity is also lowered, which is not desirable from the viewpoint of stably casting a high-quality slab. When the casting speed V is changed in this way, the solidification uniformity and the frictional restraining force are in a contradictory relationship in stably casting a high quality slab, so the casting speed V can be easily changed during operation. I can't.

  Therefore, when the present inventors diligently studied, if the conflicting frictional force and the solidification uniformity, which are in the opposite relations, can be controlled to be as constant as possible regardless of the increase or decrease in the casting speed V, excessively, Although excellent frictional restraint force or solidification uniformity cannot be obtained, neither frictional restraint force nor solidification uniformity becomes a bad value, so that cracking or breakout of the solidified shell 10 can be prevented, and a high quality slab. Has been found to be stable casting. For that purpose, the taper changing point P is moved up and down with respect to the meniscus position 11 by raising and lowering the short side mold plate 2 in the casting direction during casting according to the casting speed V, and the changing point position x is set appropriately. It has been found that if it is positioned, a sufficiently high quality slab can be cast.

For example, as shown in FIG. 9, when the continuous casting is operated under the conditions of the change point position x ₀ = 200 (mm) and the casting speed V ₀ = 1.5 (m / min), the frictional restraint force is 1.7, solidification uniformity is 0.9025. During the operation, when the casting speed V is increased from 1.5 to 2.0 (m / min), the change point position x is changed from 200 to 100 (mm) as shown by the solid line ellipse in FIG. Then, the frictional restraint force can be maintained at a low level of 1.7, and the solidification uniformity can be slightly increased from 0.9025 to 0.905 to maintain a high level. On the contrary, when the casting speed V is decreased from 1.5 to 1.0 (m / min) during operation under the above conditions, as shown by the solid oval in FIG. If the position x is changed from 200 to 300 mm, the frictional restraint force can be maintained at a low level of 1.7, and the solidification uniformity is only slightly reduced from 0.9025 to 0.90, which is still a high level. Can be maintained.

  Thus, even when the casting speed V is changed, the frictional restraining force and the solidification uniformity can be maintained substantially constant by increasing or decreasing the change point position x during casting according to the casting speed V. I understand. Therefore, in the continuous casting method according to the present embodiment, when the casting speed V increases, the short side mold plate 2 is moved upward in the casting direction during casting, and the position of the taper change point P of the short side mold plate 2 is set. Raised to approach the meniscus position 11 (that is, the change point position x is reduced). As a result, the solidification uniformity can be increased or maintained at the same level while suppressing an increase in the frictional restraining force. On the other hand, when the casting speed V decreases, the short side mold plate 2 is moved downward in the casting direction during casting, and the position of the taper change point P of the short side mold plate 2 is lowered to move away from the meniscus position 11 ( That is, the change point position x is increased). Accordingly, it is possible to suppress a decrease in solidification uniformity while reducing or maintaining the frictional restraining force.

Here, the control amount of x when the position of the taper change point P of the short side mold plate 2 is controlled to a suitable height position during casting according to the variation of the casting speed V will be described. As can be seen from the results shown in FIG. 9, the change point position may be increased by a maximum of 100 mm with respect to the increase or decrease of the casting speed V of 0.5 (m / min). The change amount of the change point position x is x / V = 100 / 0.5 = 200 (mm · min / m) or less. That is, when the casting speed V is decreased from the state of continuous casting at the casting speed V ₀ and the change point position x ₀ , the following expression (1) is satisfied, and when the casting speed V is increased, the following expression (2) is satisfied. The short side mold plate 2 may be moved up and down in the casting direction during casting so as to satisfy the above.

x ₀ <x ≦ −200 (V−V ₀ ) + x ₀ : V <V ₀ (1)
x ₀ > x ≧ −200 (V−V ₀ ) + x ₀ : V> V ₀ (2)

Further, as a realistic vertical movement amount of the short side mold plate 2 in consideration of equipment, for example, a movement amount ± 20 mm is appropriate for an increase / decrease of the casting speed V of 0.5 (m / min). At this time, the change amount of the change point position x per unit change of the casting speed V is x / V = 20 / 0.5 = 40 (mm · min / m). Therefore, when the casting speed V is increased or decreased from the state of continuous casting at the casting speed V ₀ and the change point position x ₀ , the short side mold plate 2 is being cast so as to satisfy the following expression (11). It may be moved up and down in the casting direction.
x = −40 (V−V ₀ ) + x ₀ (11)

For example, as shown in FIG. 9, the casting speed is changed from V ₀ to V from the state of continuous casting at the change point position x ₀ = 200 (mm) and the casting speed V ₀ = 1.5 (m / min). In the case of increasing or decreasing, substituting x ₀ = 200 and V ₀ = 1.5 into the above equations (1) and (2), the following equations (12) and (13) are obtained, respectively. However, for the reason described above, it is preferable that the maximum value of the change point position x is 300 mm and the minimum value is 50 mm as in the following equation (14).

200 <x ≦ 500-200V: V <1.5 (12)
200> x ≧ 500−200 V: V> 1.5 (13)
50 ≦ x ≦ 300 (14)

FIG. 10 is a diagram showing the relationship between the change point position x and the casting speed V according to the above equations (12), (13) and (14). As shown in FIG. 10, when the casting speed V is increased or decreased from the state of continuous casting at the change point position x ₀ = 200 (mm) and the casting speed V ₀ = 1.5 (m / min). Decreases or increases the change point position x so as to fall within the hatched area in FIG. As a result, the fluctuation range of the frictional restraining force and the solidification uniformity can be suppressed as compared with the case where the change point position x is not changed. In particular, during the casting according to the changed casting speed V, the changing point position x is changed to a value on or near the straight line (x = 500-200 V) in FIG. In comparison, it is possible to obtain a substantially constant frictional restraint force and solidification uniformity. Also in FIG. 10, regarding the maximum value and the minimum value of the change point position x, according to the equation (14), the maximum value of the change point position x is set to 300 mm in the range of V <1.0 according to the equation (14). In the range of V> 2.25, the minimum value of the change point position x is 50 mm.

FIG. 10 also shows a straight line of the following formula (15) obtained by substituting x ₀ = 200 and V ₀ = 1.5 into the formula (11). By changing the position x of the change point during casting according to the casting speed V in accordance with the straight line represented by the equation (15), the frictional restraining force and the solidification before and after the casting speed V is changed without overdoing the equipment. Uniformity can be maintained within a suitable range.
x = 260-40V (15)

  In addition, the timing for moving the short-side mold plate 2 in the casting direction (that is, moving up and down) according to the casting speed V as described above is as follows. In the present embodiment, the vertical movement of the short side mold plate 2 according to the casting speed V can be executed even when the injection of the molten steel into the mold 1 is interrupted or when the casting speed V becomes a steady speed after reinjection. .

  For example, first, after assembling the short side mold plate 2 and the long side mold plate 3 and installing the mold 1, before starting to inject molten steel into the mold 1, it is suitable for the average casting speed scheduled for the corresponding charge. The short-side mold plate 2 is moved up and down to the optimum position. Next, after injecting molten steel into the mold 1, the short-side mold plate 2 is moved up and down according to the actual casting speed V using the mold 1 during the casting period in which the slab is actually cast using the mold 1. It is moved to finely adjust the height position (change point position x) of the taper change point P. Thereby, after the casting speed V becomes a steady speed, the change point position x can be changed to an appropriate value in real time following the fluctuation of the casting speed V. Therefore, since the casting speed V can be flexibly dealt with, even if an intended or unexpected fluctuation in the casting speed V occurs in the actual casting period, the change point position x is optimized to produce a high quality slab. Can be cast.

  As described above, even when the casting speed V is changed, the frictional restraining force and the solidification uniformity are maintained substantially constant by increasing or decreasing the change point position x during casting according to the casting speed V. be able to. Accordingly, both the frictional restraining force and the solidification uniformity can be maintained within an appropriate range regardless of the fluctuation of the casting speed V, so that the solidification shell 100 is not cracked or broken out during casting. High quality slabs can be cast stably.

  In the above description using FIG. 9 and FIG. 10, the example of the slab width W 1100 mm, the vertical taper ratio 4.0, and the total taper ratio 1.6% / m has been described. The relationship between the restraining force and the solidification uniformity is almost the same even under other conditions (for example, the slab width is 2200 mm and the vertical taper ratio is 2.5).

[5. Continuous casting method according to carbon concentration of molten metal]
Next, a continuous casting method in which the short side mold plate 2 is moved up and down during casting according to the carbon concentration of the molten metal according to the present embodiment will be described in detail with reference to FIG. FIG. 11 shows the solidification uniformity and frictional constraint when the change point position x and the carbon concentration C of the molten metal are changed at a slab width W of 1100 mm, a vertical taper ratio of 4.0, and a total taper ratio of 1.6% / m. It is a figure which shows the change of force.

  As shown in FIG. 11, the frictional restraint force and the solidification uniformity vary depending on the type of molten steel to be cast, for example, the carbon concentration C in the molten steel. Therefore, it can be seen that the carbon concentration C is an operating condition that affects both the frictional restraining force and the solidification uniformity of the solidified shell 10 (see FIG. 2) in continuous casting. Moreover, like the casting speed V, the carbon concentration C is an operating condition that has an adverse effect on the frictional restraining force and the solidification uniformity from the viewpoint of stably casting a high-quality slab.

  That is, for example, as shown by a wavy ellipse in FIG. 11, when the carbon concentration C is 0.12 (mass%) when operating with a mold in which the change point position x is fixed to 200 mm, for example, the frictional restraint force and The solidification uniformity is the lowest, and the frictional restraining force and the solidification uniformity are the maximum when the carbon concentration C is 0.05 and 0.2.

  FIG. 12 shows the relationship between the solidification uniformity and the carbon concentration C when the change point position x is 200 mm. As shown in FIG. 12, when the carbon concentration C is near 0.12 (mass%), the solidification uniformity becomes the minimum value (for example, 0.8925). This is presumably because when the carbon concentration C is 0.12, the amount of shrinkage due to the δ → γ transformation of the molten steel is the largest. Further, the solidification uniformity gradually increases as the carbon concentration C moves away from 0.12, and when the carbon concentration C becomes 0.05 or less or 0.2 or more, the frictional restraining force and the solidification uniformity are maximum values (for example, 0). .9025), it becomes almost constant.

  As described above, both the frictional restraining force and the solidification uniformity increase or decrease according to the carbon concentration C in the molten steel. For this reason, if the carbon concentration C is changed, the solidification uniformity and the frictional restraining force are in a contradictory relationship in stably casting a high-quality slab, so it is easy to change the carbon concentration C during operation. Can not.

  Therefore, in this embodiment, similarly to the casting speed V, the short-side mold plate 2 is moved up and down in the casting direction during casting according to the carbon concentration C of the molten steel to be cast, so that the meniscus position 11 is moved. The taper change point P is moved up and down to position the change point position x at an appropriate position. As a result, it has been found that both the frictional restraining force and the solidification uniformity, which are in the opposite relations, can be controlled to be as constant as possible, so that a sufficiently high quality slab can be cast.

For example, as shown in FIG. 11, the carbon concentration C of the molten steel supplied during continuous casting of molten steel having a carbon concentration C ₀ = 0.05 (mass%) at the change point position x ₀ = 200 (mm). When increasing from 0.05 to 0.12, if the change point position x is changed from 200 to 300 (mm) as shown by a solid ellipse in FIG. 11, the frictional restraint force and the solidification uniformity are almost the same before and after the change. Can be maintained at the same level. On the other hand, the carbon concentration C of the supplied molten steel is 0 during continuous casting of molten steel with a carbon concentration C ₀ = 0.12 (mass%) at the change point position x ₀ = 300 (mm). When the value decreases from .12 to 0.05 or when C increases from 0.12 to 0.2, the change point position x is changed from 300 to 200 (mm) as shown by the solid line ellipse in FIG. By doing so, the frictional restraining force and the solidification uniformity can be maintained at substantially the same level before and after the change.

  As described above, even when the carbon concentration C is changed, the frictional restraint force and the solidification uniformity are maintained substantially constant by increasing or decreasing the change point position x during casting according to the carbon concentration C. Can do. For this reason, in the continuous casting method according to the present embodiment, the taper changing point of the short side mold plate 2 is moved by moving the short side mold plate 2 up and down in the casting direction during casting according to the increase or decrease of the carbon concentration C. P is raised or lowered to approach or move away from the meniscus position 11 (that is, the change point position x is decreased or increased).

  Specifically, for example, when the carbon concentration C is in the range of more than 0.05% by mass to less than 0.2% by mass, the short side template plate 2 is formed during casting with C = 0.12 as a peak. By moving downward in the casting direction, the taper change point P of the short side mold plate 2 is moved downward, and the change point position x is positioned at a low position. At this time, when the carbon concentration C is 0.12 mass%, the taper changing point P of the short side mold plate 2 is moved downward by 100 mm at the maximum (x = 300 mm). Further, when the carbon concentration C is 0.09 and 0.15 mass%, the taper changing point P of the short side mold plate 2 is moved downward by, for example, about 50 mm (x = 250 mm). On the other hand, when the carbon concentration C is 0.05% by mass or less, or 0.2% by mass or more, the taper change point P of the short side mold plate 2 is not moved downward and is maintained at a high position (x = 200 mm).

  In addition, as described above, the timing for moving the short-side mold plate 2 in the casting direction (that is, moving up and down) according to the steel type (for example, the carbon concentration C of the molten steel) is as follows. In general, the steel type to be injected is not suddenly changed during the casting period in which molten steel is injected into the mold 1 and the slab is actually cast using the mold 1. Therefore, in this embodiment, the vertical movement of the short side mold plate 2 according to the steel type is executed before the start of pouring of molten steel into the mold 1 or during the interruption of the pouring.

  For example, first, after assembling the short-side mold plate 2 and the long-side mold plate 3 and installing the mold 1, before injecting molten steel into the mold 1, the short-side is positioned at the optimum position suitable for the steel type of the charge. The mold plate 2 is moved up and down. Next, the corresponding charge is continuously cast in a state where the short side mold plate 2 is fixed at the optimum position. After that, when continuously casting the next charge, when the steel type of the next charge is changed from the previous steel type, the injection of the molten steel into the mold 1 is temporarily interrupted so that molten steels having different components are not mixed. To take action. When this injection is interrupted, the short side mold plate 2 is moved up and down to the optimum position suitable for the steel type of the next charge. Thereafter, the molten steel of the changed steel type is started to be reinjected into the mold 1, and the next charge is continuously cast.

  Thus, the vertical movement of the short side mold plate 2 according to the steel type is executed during a period during which the molten steel is not poured into the mold 1 during the “casting” period (that is, a period other than the actual casting period). When the steel type of the molten steel is changed as described above, the short side mold corresponding to the above-described casting speed V even when the molten steel injection is interrupted or after the casting speed V becomes a steady speed after the reinjection. It is possible to carry out a vertical movement of the plate 2.

  As described above, even when the carbon concentration C of the molten steel changes, the taper change point P of the short side mold plate 2 moves up and down during casting according to the carbon concentration C, that is, the change point position x. By increasing / decreasing the frictional force, the frictional restraining force and the solidification uniformity can be maintained substantially constant. Accordingly, both the frictional restraining force and the solidification uniformity can be maintained within an appropriate range regardless of the variation in the carbon concentration C, so that the cracks and breakout of the solidified shell 100 are not generated during casting. High quality slabs can be cast stably.

[6. Continuous casting method according to the average surface heat removal flux of the short side mold plate]
Next, with reference to FIG. 13, the continuous casting method of moving the short side mold plate 2 up and down during casting according to the surface average heat extraction flux of the short side mold plate 2 according to this embodiment will be described in detail. FIG. 13 shows the change point position x and the surface average heat flux q at the slab width W = 1100 mm, the vertical taper ratio 4.0, the total taper rate 1.6% / m, and the casting speed V = 1.5 m / min. It is a figure which shows the change of coagulation | solidification uniformity and frictional restraint force when changing.

The surface average heat removal flux q of the short side mold plate 2 is extracted from the molten metal in the mold 1 and the solidified shell 10 to the cooling water for cooling the mold 1 through the short side mold plate 2 during continuous casting. It means a value obtained by dividing the amount of heat by the area A from the meniscus position of the short side mold plate 2 to the lower end of the mold 1. The surface average heat removal flux q can be calculated by the following equation (16) from the difference between the temperature Tin when the cooling water enters the mold 1 and the temperature Tout when it exits and the flow rate Qw of the cooling water. .
q = ρ × (Tout−Tin) × Qw × Cp / A (16)
q: Surface average heat extraction flux of short side mold plate (W / m ² )
ρ: density of cooling water (kg / m ³ )
Tin: Cooling water inlet temperature (K)
Tout: Cooling water outlet temperature (K)
Qw: Cooling water flow rate (short side of mold) (m ³ / s)
Cp: Specific heat of cooling water (J / kg / K)
A: Area from the meniscus position of the short side mold plate to the lower end of the mold (m ² )
A = slab thickness D (m) × distance L (m) from the meniscus position to the lower end of the mold
The slab thickness D corresponds to the width of the short side mold plate 2.

  As shown in FIG. 13, the frictional restraining force and the solidification uniformity change according to the surface average heat removal flux q of the short side mold plate 2. Therefore, it can be seen that the surface average heat removal flux q is an operating condition that affects both the frictional restraining force and the solidification uniformity of the solidified shell 10 (see FIG. 2) in continuous casting. Moreover, the surface average heat extraction flux q is an operating condition that has an adverse effect on the frictional restraining force and the solidification uniformity from the viewpoint of stably casting a high-quality slab.

  That is, for example, as shown by the wavy ellipse in FIG. 13, when the surface average heat removal flux q increases when operating with a mold in which the change point position x is fixed at, for example, 200 mm, the solidification uniformity increases, but the friction Since the binding force also increases, it is not desirable from the viewpoint of stably casting a high-quality slab. On the other hand, if the surface average heat removal flux q decreases under the same conditions, the frictional restraining force decreases, but the solidification uniformity also decreases, which is not desirable from the viewpoint of stably casting a high-quality slab. . When the surface average heat extraction flux q changes in this way, the solidification uniformity and the frictional restraining force are in a contradictory relationship in stably casting a high-quality slab, so the surface average heat extraction flux q during operation. It is preferable to take measures according to changes in

  Therefore, when the present inventors diligently studied, it is possible to control the frictional restraining force and the solidification uniformity, which are in the opposite relations, to be as constant as possible regardless of the increase or decrease of the surface average heat removal flux q. Although the frictional restraining force or solidification uniformity that is excessively excellent cannot be obtained, neither the frictional restraining force nor the solidification uniformity is a bad value, so that the solidified shell 10 can be prevented from cracking, breakout, etc. It was found that the slab can be stably cast. For this purpose, the taper changing point P is moved up and down with respect to the meniscus position 11 by raising and lowering the short side mold plate 2 in the casting direction during casting according to the surface average heat removal flux q, and the changing point position x It has been found that a sufficiently high quality slab can be cast if is positioned at an appropriate position.

For example, as shown in FIG. 13, the change point position x ₀ = 200 (mm), and the surface average heat removal flux q is the reference value q ₀ (for example, q ₀ = 1.2 × 10 ⁶ (W / m ² )). When the continuous casting is operated under these conditions, the frictional restraining force is 1.7 and the solidification uniformity is 0.9025. Here, when the distance L from the meniscus position to the lower end of the mold 1 is 0.8 m and the casting speed V is 1.5 m / min, the reference value q ₀ of the surface average heat removal flux q is expressed by the following equation (17). The approximate value is as follows.
q ₀ = 1.0 × 10 ⁶ × (0.8 / 1.5) ^−0.344 = 1.2 × 10 ⁶ (W / m ² )

During the operation, when the surface average heat removal flux q increases from q ₀ to q ₁ (for example, q ₁ = 1.3 × 10 ⁶ (W / m ² ), q ₁ / q ₀ = 1.1). As shown by the solid ellipse in FIG. 13, if the change point position x is changed from 200 to 100 (mm), the frictional restraint force can be maintained at a low level of 1.7, and the solidification uniformity is 0. Slightly increased from 9025 to 0.905 to maintain a high level. Conversely, when the surface average heat removal flux q decreases from q ₀ to q ₂ during operation under the above conditions (for example, q ₂ = 1.0 × 10 ⁶ (W / m ² )). , Q ₂ / q ₀ = 0.87), and as shown by the solid line ellipse in FIG. 13, if the change point position x is changed from 200 to 300 mm, the frictional restraint force remains 1.7 and can be maintained at a low level. At the same time, the solidification uniformity is only slightly reduced from 0.9025 to 0.90, and can still be maintained at a high level.

  Thus, even when the surface average heat removal flux q of the short side mold plate 2 changes, the frictional restraint can be achieved by increasing or decreasing the change point position x during casting according to the surface average heat removal flux q. It can be seen that the force and solidification uniformity can be maintained almost constant. Therefore, in the continuous casting method according to the present embodiment, when the surface average heat removal flux q increases, the short side mold plate 2 is moved upward in the casting direction during casting, and the taper change point P of the short side mold plate 2 is reached. Is raised and brought closer to the meniscus position 11 (that is, the change point position x is made smaller). As a result, the solidification uniformity can be increased or maintained at the same level while suppressing an increase in the frictional restraining force. On the other hand, when the surface average heat removal flux q decreases, the short side mold plate 2 is moved downward in the casting direction during casting, and the position of the taper change point P of the short side mold plate 2 is lowered to move from the meniscus position 11. Move away (that is, increase the change point position x). Accordingly, it is possible to suppress a decrease in solidification uniformity while reducing or maintaining the frictional restraining force.

Here, the control of x when the position of the taper change point P of the short side mold plate 2 is controlled to a suitable height position during casting according to the fluctuation of the surface average heat removal flux q of the short side mold plate 2. The amount will be described. As can be seen from the results of FIG. 13, for example, when the surface average heat removal flux q is increased or decreased by 10% with respect to the reference value q ₀ , the change point position may be decreased by 100 mm at the maximum. However, for the reasons described above, it is preferable that the maximum value of the change point position x is 300 mm and the minimum value is 50 mm.

In addition, the surface average heat extraction flux q (W / m ² ) through the short side mold plate 2 is the temperature difference between the inlet side and the outlet side of the cooling water for cooling the short side mold plate 2 or the short side mold. It can be calculated from the detected value of a temperature difference sensor (for example, a thermocouple) provided on the plate 2. Further, the surface average heat removal flux q (W / m ² ) varies depending on the steel type and casting conditions. For example, the casting speed V (m / min) and the distance L (m) from the meniscus position to the lower end of the mold are determined. It is calculated | required by the following formula | equation (17) as a parameter.
q = 1.0 * 10 ⁶ * (L / V) ^−0.344 (17)

  Furthermore, the surface average heat removal flux q increases or decreases according to the casting speed V. For example, if the casting speed V decreases, the surface average heat extraction flux q decreases. However, even in a steady state where the casting speed V is constant, the surface average heat removal flux q sometimes changes. For example, when the inflow state of powder input for lubrication between the mold 1 and the solidified shell 10 (slab) changes, the surface average heat removal flux q varies depending on the thickness of the powder. The surface average heat removal flux q also varies depending on the contact state between the short side mold plate 2 of the mold 1 and the solidified shell 10 (slab). Thus, even if the casting speed V is constant, the surface average heat extraction flux q may fluctuate due to unsteady factors. In this case, if the change point position x is controlled during casting in accordance with the increase or decrease of the surface average heat removal flux q as described above, the solidification uniformity can be maintained without increasing the frictional restraining force.

  Further, as described above, the timing for moving the short-side mold plate 2 in the casting direction (that is, moving up and down) according to the surface average heat extraction flux q is as follows. In this embodiment, the change of the change point position x in accordance with the surface average heat extraction flux q can be performed even when the molten steel injection into the mold 1 is interrupted or when the surface average heat extraction flux q is in a steady state after reinjection. It is feasible.

First, in the continuous casting apparatus, for each steel type and casting condition, the temperature difference of the cooling water during casting, the detection value of the thermocouple, etc. are measured, and the standard of the surface average heat removal flux q of the short side mold plate 2 is measured. setting the value q ₀ in advance. Next, after assembling the short side mold plate 2 and the long side mold plate 3 and installing the mold 1, before starting to inject molten steel into the mold 1, depending on the steel type and casting conditions scheduled for the corresponding charge Then, the optimum surface average heat extraction flux q is obtained, and the short side mold plate 2 is arranged so as to have a height suitable for the surface average heat extraction flux q. Next, after the start of pouring of molten steel into the mold 1, the measurement is performed while actually measuring the surface average heat removal flux q of the short-side mold plate 2 during the casting period in which the slab is actually cast using the mold 1. The short side mold plate 2 is moved up and down according to the surface average heat removal flux q, and the height position (change point position x) of the taper change point P is finely adjusted. Thereby, after the casting speed V becomes a steady speed, the change point position x can be changed to an appropriate value in real time following the fluctuation of the surface average heat removal flux q. Therefore, since it is possible to flexibly cope with the fluctuation of the surface average heat removal flux q, even if the fluctuation of the surface average heat removal flux q due to the unsteady factor occurs in the actual casting period, the change point position x is optimized, High quality slabs can be cast.

  As described above, even when the surface average heat removal flux q varies, the frictional restraint force and the solidification uniformity can be increased by increasing or decreasing the change point position x during casting according to the surface average heat removal flux q. Can be maintained substantially constant. Accordingly, both the frictional restraining force and the solidification uniformity can be maintained within an appropriate range regardless of the fluctuation of the surface average heat removal flux q, so that the solidified shell 100 is cracked or broken out during casting. High quality slabs can be cast stably.

  In the description with reference to FIG. 13 described above, an example in which the slab width W1100 mm, the vertical taper ratio 4.0, the total taper rate 1.6% / m, and the casting speed V = 1.5 m / min has been described. The relationship between the change point position x, the frictional restraint force, and the solidification uniformity is substantially the same even under other conditions (for example, a slab width of 2200 mm and an upper and lower taper ratio of 2.5 can be exemplified).

[7. Configuration of continuous casting equipment]
Next, the continuous casting apparatus which performs the continuous casting method which concerns on this embodiment mentioned above is demonstrated. FIG. 14 is a diagram illustrating a configuration of a continuous casting apparatus according to the present embodiment. In FIG. 14, for convenience of explanation, only the configuration around the short side mold plate 2 on one side of the continuous casting apparatus is shown, but it is assumed that the other side also has a symmetric configuration.

As shown in FIG. 14, the continuous casting apparatus according to the present embodiment includes a continuous casting mold 1 (hereinafter also referred to as “mold 1”) and a short-side drive mechanism 4. The mold 1 includes a pair of multi-step tapered short side mold plates 2 having two or more short side taper ratios (unit:% / m) different in the casting direction, and the pair of short side mold plates 2 from both sides in the width direction. It consists of a pair of long-side mold plates 3 (not shown in FIG. 14; see FIG. 3). The long-side mold plate 3 and the short-side mold plate 2 are each configured as a pair, and the side facing the solidified shell 10 is preferably a water-cooled copper plate 2a, and the opposite surface is a steel back frame 2b. The width of the short side mold plate 2 is substantially equal to the thickness of the cast slab to be cast, and the distance between the lower ends of the pair of short side mold plates 2 is substantially equal to the width of the cast slab (slab width). Tapered surface 6 of the short side mold plate 2, and the upper tapered surface 6 _U taper ratio is large, consists of a lower tapered surface 6 taper ratio is small _L (upper taper ratio T _U> lower tapered index T _L), the upper tapered The boundary between the surface 6 _U and the lower taper surface 6 _L is a taper change point P. The pair of short side mold plates 2 are arranged to face each other and sandwiched between the pair of long side mold plates 3, thereby forming the mold 1 having a rectangular casting space.

  The short side drive mechanism 4 is, for example, for moving the short side mold plate 2 horizontally or tilting, and for moving the short side mold plate 2 in the casting direction (that is, moving up and down in the vertical direction). And the control device 5 for controlling the actuators 7, 8, 9. For example, as shown in the drawing, an electric cylinder, a hydraulic cylinder, or the like can be used as the actuators 7, 8, and 9. Also good.

  The two actuators 7 and 8 for horizontal movement and tilting are respectively installed on the upper and lower surfaces of the movable base 20 in a substantially horizontal posture. The tips of the actuators 7 and 8 are connected to the upper side and the lower side of the back frame 2b of the short side mold plate 2 by hinges 21 and 22, respectively. The upper and lower two-stage actuators 7 and 8 support the short-side mold plate 2 from the back frame 2b side. The movable base 20 supports these actuators 7 and 8, and a connecting member 23 is fixed to the rear end of the movable base 20. The connecting member 23 includes a horizontal portion 23a and a vertical portion 23b, and has an L-shaped cross-sectional shape.

  The actuator 9 is disposed in a substantially vertical posture between the connecting member 23 and the fixed base 24. The upper end of the actuator 9 is rotatably connected to the lower surface side of the horizontal portion 23 a of the connecting member 23 by a hinge portion 25, and the lower end of the actuator 9 is rotated to the upper surface of the fixed base 24 by a hinge portion 26. Connected as possible. The hinge connection between the upper end and the lower end of the actuator 9 is not a mechanical requirement. For example, if the connection member 23, the guide plate 27, and the elevating guide portion 28 have sufficient rigidity, the hinge connection as shown in the drawing is used. The upper end and the lower end of the actuator 9 may be fixedly connected to the connecting member 23 and the fixed base 24 without using the above.

  A guide plate 27 is erected on the front side of the fixed base 24. The guide plate 27 has a function of guiding the vertical movement of the vertical portion 23 b of the connecting member 23. The guide plate 27 and the connecting member 23 function as an elevating guide portion 28 for guiding the elevating of the short side mold plate 2.

  As shown in FIG. 15, the control device 5 includes an input unit 31, an optimum value calculation unit 32, and a drive control unit 33. The input unit 31 is configured by a computer device or the like operated by an operator, and inputs set values of various operating conditions related to continuous casting from the operator and various sensors. The input unit 31 sends the set value of the input operation condition to the optimum value calculation unit 32. Based on the setting value of the operation condition from the input unit 31, the optimum value calculation unit 32 is configured to determine the optimum value related to the arrangement of the short side mold plate 2 according to the operation condition (for example, the width between the two short side mold plates 2). , The height position of the short side mold plate 2, the amount of inclination, etc.) are calculated. The optimum value calculation unit 32 sends the calculated optimum value to the drive control unit 33. The drive control unit 33 calculates a control amount for driving the actuators 7, 8, 9 based on the optimum value from the optimum value calculation unit 32, and outputs the control amount to the actuators 7, 8, 9. The actuators 7, 8, and 9 are driven based on a control amount from the control device 5.

  Next, the operation of the short side drive mechanism 4 configured as described above will be described. The control device 5 of the short-side drive mechanism 4 uses the actuators 7 and 8 so that the short-side mold plate 2 is appropriately arranged (width, height, inclination between short sides) based on the input operating conditions. , 9 are driven.

  For example, the control device 5 drives the actuators 7 and 8 by an appropriate amount to move the short-side mold plate 2 in the horizontal direction to control the width between the two short-side mold plates 2 or The side mold plate 2 can be tilted to control the inclination (total taper ratio) of the short side mold plate 2. By determining the position of the short-side mold plate 2 by the movement of the upper and lower two-stage actuators 7 and 8, the total taper rate of the short-side mold plate 2 is set to a predetermined value for each set slab width W. Can do. In the present embodiment, from the viewpoint of a practical operation mode, the same total taper ratio is set in any slab width W during casting, and the vertical taper ratio is 4 or less in any slab width W. Moreover, it is preferable to control the horizontal position and inclination of the short side mold plate 2.

  Further, the short side drive mechanism 4 according to the present embodiment includes not only the horizontal drive mechanism and the tilt drive mechanism of the short side mold plate 2 as described above, but also a lifting mechanism for the short side mold plate 2. It is correct. That is, the control device 5 of the short side drive mechanism 4 moves the short side mold plate 2 in the casting direction (that is, moves up and down) by driving the actuator 9 by an appropriate amount according to the operating conditions. The height of the taper changing point P of the short side mold plate 2, that is, the changing point position x can be controlled.

  Specifically, the control device 5 of the short side drive mechanism 4 is in accordance with the operating conditions such as the casting speed V, the type of molten steel (for example, carbon concentration C), the surface average heat removal flux q of the short side mold plate 2 and the like. Then, an appropriate value of the change point position x with respect to the meniscus position is calculated, a height position of the short side mold plate 2 such that the change point position x becomes the appropriate value is obtained, and further, the short side mold plate 2 has the height. The actuator 9 is driven and controlled so as to be in the position. As a result, when the actuator 9 is driven, the movable base 23 moves up and down while being guided by the guide plate 27, and the short side mold plate 2 connected to the movable base 23 via the actuators 7 and 8 moves up and down. , Positioned at the height position.

  In this way, the short-side drive mechanism 4 is configured so that the short-side mold plate 2 is cast during casting according to the continuous casting operation conditions such as the casting speed V, the type of molten steel, and the surface average heat removal flux q of the short-side mold plate 2. Can be moved to a suitable position in the casting direction. Therefore, the continuous casting method according to the present embodiment described above can be suitably realized.

  Next, a modified example of the continuous casting apparatus will be described with reference to FIG. FIG. 16 is a diagram illustrating a configuration of a continuous casting apparatus according to a modified example of the present embodiment. In FIG. 16, for convenience of explanation, only the configuration around the short side mold plate 2 on one side of the continuous casting apparatus is shown, but it is assumed that the other side also has a symmetric configuration.

  As shown in FIG. 16, the continuous casting apparatus according to the modified example of the present embodiment also has a mold 1 composed of a pair of short side mold plates 2 and a pair of long side mold plates 3, and a short side, as in FIG. 14. And a drive mechanism 40. The short side drive mechanism 40 is, for example, for moving the short side mold plate 2 horizontally or tilting, and for moving the short side mold plate 2 in the casting direction (that is, moving up and down in the vertical direction). And the control device 5 for controlling these actuators 47, 48, 49. The actuators 47, 48, and 49 can be electric cylinders, hydraulic cylinders, etc. as shown in the figure, but are not limited to such examples, and the short-side drive mechanism uses any drive device such as an electric motor. Also good. The configuration of the control device 5 is the same as that shown in FIG.

  The two actuators 47 and 48 for horizontal movement and tilting are each supported by the support frame 51 on the fixed base 50. The movable base 52 includes a back surface portion 52a, a bottom portion 52b, and a front surface portion 52c, and has a substantially U-shaped cross-sectional shape. The tips of the actuators 47 and 48 are connected to the upper side and the lower side of the back surface 52a of the movable base 52 by hinges 53 and 54, respectively. On the other hand, a connecting portion 55 is attached to the back side of the short side mold plate 2. The connecting member 55 includes a horizontal portion 55a and a vertical portion 55b, and has an L-shaped cross-sectional shape.

  The actuator 49 is disposed in a substantially vertical posture between the connecting member 55 and the movable base 52. The upper end of the actuator 49 is rotatably connected to the lower surface side of the horizontal portion 55 a of the connecting member 55 by a hinge portion 56, and the lower end of the actuator 49 is a hinge portion to the upper surface of the bottom surface portion 52 b of the movable base 52. 57 is rotatably connected. It should be noted that the upper and lower hinges of the actuator 49 can be fixedly connected in the same manner as the actuator 9 shown in FIG. In addition, the front surface portion 52 c erected on the front surface side of the movable base 52 functions as a guide plate that guides the vertical movement of the vertical portion 55 b of the connecting member 55. The movable base 52 and the connecting member 23 function as an elevating guide part 58 for guiding the elevating of the short side mold plate 2.

  Next, the operation of the short side drive mechanism 40 having the above configuration will be described. The control device 5 of the short side drive mechanism 40 uses the actuators 47 and 48 so that the short side mold plate 2 is appropriately arranged (width, height, inclination between short sides) based on the input operating conditions. , 49 are driven.

  For example, the control device 5 drives the actuators 47 and 48 by an appropriate amount to move the short side mold plate 2 in the horizontal direction to control the width between the two short side mold plates 2 or The side mold plate 2 can be tilted to control the inclination (total taper ratio) of the short side mold plate 2. Further, the short side drive mechanism 40 shown in FIG. 16 is not limited to the horizontal drive mechanism and the tilt drive mechanism of the short side mold plate 2 as in the short side drive mechanism 4 shown in FIG. It is characterized by having an elevating mechanism. That is, the control device 5 of the short-side drive mechanism 40 drives the actuator 49 by an appropriate amount to move the short-side mold plate 2 in the casting direction (that is, move up and down in the up-and-down direction). The height of the second taper change point P, that is, the change point position x can be controlled.

  Specifically, the control device 5 of the short side drive mechanism 40 depends on operating conditions such as the casting speed V, the type of molten steel (for example, carbon concentration C), the surface average heat removal flux q of the short side mold plate 2 and the like. Then, an appropriate value of the change point position x with respect to the meniscus position is calculated, a height position of the short side mold plate 2 such that the change point position x becomes the appropriate value is obtained, and further, the short side mold plate 2 has the height. The actuator 49 is driven and controlled so that the position is reached. As a result, the driving of the actuator 49 causes the connecting member 55 to move up and down while being guided by the front surface portion 52b of the fixed base 52, and the short-side mold plate 2 connected to the connecting member 55 moves up and down to raise the height. Positioned to position.

  As described above, the short-side drive mechanism 40 shown in FIG. 16 is similar to the short-side drive mechanism 40 shown in FIG. 14 in terms of the casting speed V, the type of molten steel, and the surface average heat removal flux of the short-side mold plate 2. The short side mold plate 2 can be moved to a suitable position in the casting direction during casting according to the continuous casting operating conditions such as q. Therefore, the continuous casting method according to the present embodiment described above can be suitably realized.

  When changing the slab width W during continuous casting, it is required to continuously change the slab width W while performing normal casting. During such a width change, it is necessary to change the total taper rate to perform a smooth width change, and the total taper rate cannot be kept constant.

  The continuous casting apparatus according to the present embodiment can cast a slab having a wide range from a minimum castable slab width of 1100 mm or less to a maximum castable slab width of 2200 mm or more. For example, the minimum castable slab width is preferably 800 mm or less, and, for example, 600 mm is practical. The maximum castable slab width is realistic, for example, 2500 mm.

[8. effect]
In the above, the continuous casting method which concerns on this embodiment, and the continuous casting apparatus which implement | achieves it were demonstrated. According to this embodiment, the short-side mold plate 2 during casting depends on the operating conditions such as the casting speed V or the type of molten metal (for example, carbon concentration C), the surface average heat removal flux q of the short-side mold plate 2 and the like. Is moved in the casting direction (up and down in the vertical direction), the position of the taper change point P of the short side mold plate 2 is moved up and down with respect to the meniscus position 11, and the change point position x is increased or decreased. As a result, the position of the taper change point P of the short side mold plate 2 is moved up and down while the meniscus position 11 in the mold 1 is kept at a fixed position, so that it is appropriate to cope with fluctuations in operating conditions such as the casting speed V. It can be positioned at the change point position x.

  Therefore, before and after the change of the operating conditions, both the solidification uniformity and the frictional restraining force that are in a reciprocal relationship can be controlled to be substantially constant values. It is possible to cope with changes in operating conditions such as casting speed while satisfying the above restrictions. Therefore, regardless of the casting conditions such as casting speed V, high quality casting without surface cracks and internal cracks while eliminating the solidification unevenness of the slab and ensuring the solidified shell thickness is more than the limit thickness of the breakout. The piece can be cast stably.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  For example, in the above-described embodiment, an example of a two-step taper short-side mold plate has been described as the multi-step taper short-side mold plate.

  In the above embodiment, the operating conditions affecting both the solidification uniformity and the frictional restraining force of the solidified shell 10 include the casting speed V, the carbon concentration C of the molten steel metal, and the surface average heat removal flux of the short side mold plate 2. An example of q is described, and an example in which the taper change point P of the short side mold plate 2 is raised and lowered during casting according to the casting speed V, the carbon concentration C or the surface average heat removal flux q has been described. It is not limited to such an example. For example, the taper change point of the short side mold plate may be raised or lowered during casting according to superheat (heating temperature of molten steel), slab width W, or the like as the operation condition. When the super heat is high, the shell thickness of the solidified shell during continuous casting becomes thin. Therefore, it is possible to raise the temperature of the molten metal at the casting limit by raising and lowering the taper change point of the short side mold plate during casting according to superheat.

DESCRIPTION OF SYMBOLS 1 Continuous casting mold 2 Multistage taper short side mold plate 3 Long side mold plate 4, 40 Short side drive mechanism 5 Controller 6 Tapered surface 6 _U upper taper surface 6 _L lower taper surface 7, 8, 9, 47, 48, 49 Actuator 10 Solidified shell 11 Meniscus position P Taper change point

Claims (20)

Continuous casting method using a mold comprising a pair of multi-step taper short side mold plates having two or more tapers different in casting direction and a pair of long side mold plates sandwiching the multi-step taper short side mold plate from both sides in the width direction In
By moving the multistage tapered short side mold plate in the casting direction during casting, the solidification uniformity of the solidified shell of the molten metal in the mold and the friction between the solidified shell and the multistage tapered short side mold plate The position of the taper change point of the multi-stage tapered short side mold plate is moved relative to the meniscus position of the molten metal in the mold in the casting direction so as to maintain both of the restraining forces substantially constant. , Continuous casting method.   2. The continuous casting method according to claim 1, wherein the multistage tapered short side mold plate is moved in a casting direction during casting in accordance with operating conditions of continuous casting.   The continuous casting operation condition is an operation condition that affects both the solidification uniformity of the solidified shell solidified by the molten metal and the frictional restraint force between the solidified shell and the multi-stage tapered short side mold plate. The continuous casting method according to claim 2, wherein the method is a continuous casting method. The continuous casting operating conditions include casting speed,
4. The continuous casting method according to claim 2, wherein the multi-stage tapered short side mold plate is moved in a casting direction during casting according to the casting speed.   The multi-stage tapered short side mold plate is moved upward in the casting direction during casting according to the increase in the casting speed, and the multi-stage tapered short side mold plate is moved downward in the casting direction during casting according to the decrease in the casting speed. The continuous casting method according to claim 4, wherein: The continuous casting operating conditions include the carbon concentration of the molten metal,
The continuous casting method according to any one of claims 2 to 5 , wherein the multistage tapered short side mold plate is moved in a casting direction during casting according to a carbon concentration of the molten metal. The operating conditions of the continuous casting include the surface average heat removal flux of the multi-stage tapered short side mold plate,
The continuous casting method according to any one of claims 2 to 6 , wherein the multistage tapered short side mold plate is moved in a casting direction during casting according to the surface average heat removal flux. The multi-stage tapered short side mold plate is moved upward in the casting direction during casting according to the increase in the surface average heat extraction flux, and the multi-stage taper short side mold plate during casting according to the decrease in the surface average heat extraction flux. The continuous casting method according to claim 7 , wherein the casting is moved downward in the casting direction. A mold comprising a pair of multi-stage taper short side mold plates having two or more tapers different from each other in the casting direction, and a pair of long side mold plates sandwiching the multi-stage taper short side mold plate from both sides in the width direction;
By moving the multistage tapered short side mold plate in the casting direction during casting, the solidification uniformity of the solidified shell of the molten metal in the mold and the friction between the solidified shell and the multistage tapered short side mold plate A short-side drive mechanism that moves the position of the taper change point of the multi-stage tapered short-side mold plate relative to the meniscus position of the molten metal in the mold in the casting direction so as to maintain both of the restraining forces substantially constant ; ,
A continuous casting apparatus comprising: The continuous casting apparatus according to claim 9 , wherein the short side drive mechanism moves the multi-stage tapered short side mold plate in a casting direction during casting according to an operation condition of continuous casting. The continuous casting operation condition is an operation condition that affects both the solidification uniformity of the solidified shell solidified by the molten metal and the frictional restraint force between the solidified shell and the multi-stage tapered short side mold plate. The continuous casting apparatus according to claim 10 , wherein the apparatus is a continuous casting apparatus. The continuous casting operating conditions include casting speed,
The continuous casting apparatus according to claim 10 or 11 , wherein the short side drive mechanism moves the multi-stage tapered short side mold plate in a casting direction during casting according to the casting speed. The short side drive mechanism moves the multi-stage tapered short side mold plate upward in the casting direction during casting according to an increase in the casting speed, and the multi-stage tapered short side mold during casting according to a decrease in the casting speed. The continuous casting apparatus according to claim 12 , wherein the plate is moved downward in the casting direction. The continuous casting operating conditions include the carbon concentration of the molten metal,
The short side drive mechanism moves the multi-stage tapered short side mold plate in the casting direction during casting according to the carbon concentration of the molten metal, according to any one of claims 10 to 13. Continuous casting equipment. The operating conditions of the continuous casting include the surface average heat removal flux of the multi-stage tapered short side mold plate,
The short-side drive mechanism moves the multi-stage tapered short-side mold plate in a casting direction during casting according to the surface average heat removal flux, according to any one of claims 10 to 14. Continuous casting equipment. The short side drive mechanism moves the multi-stage tapered short side mold plate upward in the casting direction during casting according to an increase in the surface average heat extraction flux, and during casting according to a decrease in the surface average heat extraction flux. The continuous casting apparatus according to claim 15 , wherein the multi-stage tapered short side mold plate is moved downward in the casting direction.   Continuous casting method using a mold comprising a pair of multi-step taper short side mold plates having two or more tapers different in casting direction and a pair of long side mold plates sandwiching the multi-step taper short side mold plate from both sides in the width direction In
  The position of the taper change point of the multistage tapered short side mold plate is moved with respect to the meniscus position of the molten metal in the mold by moving the multistage tapered short side mold plate in the casting direction during casting according to the casting speed. Move relative to the casting direction,
  When the distance from the meniscus position to the taper changing point of the multistage tapered short side mold plate is x (mm) and the casting speed is V (m / min),
  Casting speed V ₀ , Change point position x ₀ From the state of continuous casting at ₀ In the case of decreasing from V to V, the following formula (1) is satisfied, and the casting speed is set to V ₀ In the case of increasing from V to V, the continuous casting method is characterized in that the multi-stage tapered short side mold plate is moved in the casting direction during casting so as to satisfy the following expression (2).
    x ₀ <X ≦ −200 (V−V ₀ ) + X ₀   : V <V ₀   (1)
    x ₀ > X ≧ −200 (V−V ₀ ) + X ₀   : V> V ₀   (2)   A mold comprising a pair of multi-stage taper short side mold plates having two or more tapers different from each other in the casting direction, and a pair of long side mold plates sandwiching the multi-stage taper short side mold plate from both sides in the width direction;
  The position of the taper change point of the multistage tapered short side mold plate is moved with respect to the meniscus position of the molten metal in the mold by moving the multistage tapered short side mold plate in the casting direction during casting according to the casting speed. A short-side drive mechanism for relative movement in the casting direction;
With
  When the distance from the meniscus position to the taper changing point of the multistage tapered short side mold plate is x (mm) and the casting speed is V (m / min),
  Casting speed V ₀ , Change point position x ₀ From the state of continuous casting at ₀ In the case of decreasing from V to V, the following formula (1) is satisfied, and the casting speed is set to V ₀ When increasing from V to V, the continuous casting apparatus is characterized in that the multi-stage tapered short side mold plate is moved in the casting direction during casting so as to satisfy the following expression (2).
    x ₀ <X ≦ −200 (V−V ₀ ) + X ₀   : V <V ₀   (1)
    x ₀ > X ≧ −200 (V−V ₀ ) + X ₀   : V> V ₀   (2)   Continuous casting method using a mold comprising a pair of multi-step taper short side mold plates having two or more tapers different in casting direction and a pair of long side mold plates sandwiching the multi-step taper short side mold plate from both sides in the width direction In
  The position of the taper change point of the multi-stage tapered short side mold plate is moved in the casting direction during casting according to the carbon concentration of the molten metal, so that the meniscus position of the molten metal in the mold Relative to the casting direction
  When the carbon concentration C (mass%) of the molten metal is 0.05 <C <0.2, the multistage taper is shorter during casting than when C ≦ 0.05 or C ≧ 0.2. A continuous casting method, wherein the side mold plate is moved downward in the casting direction.   A mold comprising a pair of multi-stage taper short side mold plates having two or more tapers different from each other in the casting direction, and a pair of long side mold plates sandwiching the multi-stage taper short side mold plate from both sides in the width direction;
  The position of the taper change point of the multi-stage tapered short side mold plate is moved in the casting direction during casting according to the carbon concentration of the molten metal, so that the meniscus position of the molten metal in the mold A short side drive mechanism that moves relative to the casting direction with respect to,
With
  When the carbon concentration C (mass%) of the molten metal is 0.05 <C <0.2, the multistage taper is shorter during casting than when C ≦ 0.05 or C ≧ 0.2. A continuous casting apparatus, wherein the side mold plate is moved downward in the casting direction.

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