JP3016176B2 - Slab width changing method in continuous casting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a technique for changing the width of a slab produced by continuous casting during casting.

[0002]

2. Description of the Related Art Molten steel is poured from above into a mold (water-cooled mold with no bottom), a solidified shell layer is formed on the mold surface of the mold, and the obtained slab is continuously drawn downward from the mold. 2. Description of the Related Art Continuous casting equipment that produces long cast slabs by holding a group and performing predetermined cooling is widely used. In addition, the technique of changing the cross-sectional dimension of a slab during casting has been put to practical use because of the necessity of approaching the shape of the product and increasing the yield. The target slab of the present invention has a rectangular cross-section, and the mold for that is composed of two long-side molds (fixed) and two short-side molds (movable), and the short-side mold is moved to change the cross section. It is to do.

A technique for moving a short side mold is disclosed in
No. 0-68137, "Continuous casting method of variable width of steel",
Japanese Patent Application Laid-Open No. Hei 3-133549, "Method of changing slab width during continuous casting", and the like are known. That is, in the above, the reduced moving section of the mold is divided into a forward inclined section, a parallel moving section, and a backward inclined section, and the moving speed of the upper end portion of the short side mold is Vt, and the moving speed of the lower end portion is Vb ( V: speed, t: top, b: bottom), Vt> Vb in the forward leaning section, Vt = Vb in the parallel moving section, and Vt <Vb in the backward leaning section.
It is characterized by the following.

[0004] The above description is based on the assumption that the reduced moving section of the mold is divided into a forward leaning phase, a steady moving phase, and a backward leaning phase, and the moving speed of the upper end of the short side mold is Vt and the moving speed of the lower end is Vb. To
Vt> Vb in the forward leaning period and the steady moving period, and Vt in the backward leaning period.
It is characterized in that t <Vb. Are excluded. In order to differentiate Vt and Vb,
In the above, the short side mold is provided with upper and lower cylinders, and the short side mold is advanced, retracted, and inclined by these two upper and lower cylinders.

[0005]

In recent years, the demand for higher productivity has led to an increase in the speed of drawing a slab, that is, an increase in the casting speed. It was found that the plating applied to the casting surface was likely to be peeled off, and that the slab was likely to cause surface cracks and breakout (leakage of hot water).

[0006]

The inventor of the present invention has continuously studied the formation of a solidified shell layer on a casting surface.
For example, Japanese Patent Application Laid-Open No. 247059 proposed a tapered casting surface. Based on this research and experience, it is considered that the cause of the above-mentioned peeling of the plating, surface cracks of the slab, and breakout may be that the short-side mold described above does not match the solidified shell layer. From the standpoint of solving this problem, an improvement method has been invented.

More specifically, in a slab width changing method for changing the width of a slab from a wide width to a narrow width or from a narrow width to a wide width without interrupting a pouring operation, a short side mold is formed under the following conditions. It is characterized by moving. The lower part of the short side mold is
Move at a predetermined speed. In the upper part of the short side mold, the first half of the movement is greater than the predetermined speed and 130 mm / min.
It moves at a high speed which is the limit, and moves in the latter half of the movement at a speed lower than the predetermined speed. The short-side mold shape after the movement is matched with the short-side mold shape before the movement. "K" while moving the mold
The upper part of the short side mold is curved in a letter shape.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. The drawings should be viewed in the direction of reference numerals. FIG. 1 is a principle view of a width changing device according to the present invention. The width changing device 1 includes an upper cylinder 3, a center cylinder 4, and a lower cylinder 5 locked at an upper portion, a center portion, and a lower portion of a short side mold 2. Control unit 6 for comprehensively controlling the cylinders 3, 4, and 5
Consists of

Next, the operation of the above-described width changing device will be described. 2 (a) to 2 (e) are movement diagrams (short width) of the short side mold according to the method of the present invention, in which the moving speed of the upper cylinder 3 is V1, the moving speed of the central cylinder 4 is V2, and the lower speed is V2. To change the moving speed of the cylinder 5 to V3 and change the short side mold 2 from a wide width to a narrow width, first, V2 = V3, V2 <V
Under the condition (1), the short side mold 2 of (a) is advanced in the direction of the arrow. In (b), since the upper part of the short side mold 2 precedes the center part and the lower part, it is curved forward by α, and further, in (c), which corresponds to the movement middle point, the upper part is β (where α <
Bend only by β). Thus, the central portion of the short side mold 2 is located behind the line 8 connecting the upper portion and the lower portion.
From (c), the condition is changed to V2 = V3, V1 <V2. That is, the upper part is slower than the central part and lower part,
In (d), the curvature of the upper portion returns to approximately α, and in (e), the curvature is eliminated, and the shape becomes the same as that of (a).

Next, a comparison between the method of the present invention and the conventional method will be described. Common experimental conditions: Casting speed 3.0-5.0 m / min Steel grade Low carbon aluminum killed steel Mold size 1000 mm long side, 100 mm short side, 900 mm height Mold cooling Cooling water, flow rate 9.0 m / s Mold initial inclination 1 0.1% / m Experimental equipment The present invention is shown in FIG.
Compliant with Japanese Patent No. 68137, "Variable steel continuous casting method".

FIG. 3 is a graph showing the occurrence of hot water leakage and cracking in the method of the present invention and the conventional method. The horizontal axis represents the width changing speed (m).
m / min), the vertical axis is the index of molten metal leak / crack occurrence (m / m)
It is. The index of molten metal leak / crack occurrence is the cumulative length of molten metal leak / crack generated per unit length of the slab surface, and depends on the casting speed, mold inclination angle (taper angle), mold cooling, steel type and width change speed. Also fluctuate.

In the conventional method, the width changing speed is 10 mm / min.
Over 40mm / m.
In the index of leak and crack occurrence 0.5, 50mm / min
To reach a molten metal leak / crack occurrence index of 1.0. On the other hand, in the method of the present invention, a molten metal leak / crack starts to be generated at a speed exceeding 130 mm / min, a molten metal leak / crack generation index of 0.5 at 150 mm / min, and a molten metal leak / crack index of 1.0 at 160 mm / min. Reach Therefore, according to the present invention, the width changing speed can be greatly increased.

When the width change is performed during casting, a tapered portion (a portion where the width gradually changes) is set between the wide width and the narrow width of the slab.
Occurs. Since the casting speed is constant, the length of the taper increases as the width changing speed decreases. The tapered portion is a portion to be subjected to shape correction in a later rolling stage. If the tapered portion is long, the correction work increases, which is not preferable. In this regard, the present invention is extremely advantageous because the width changing speed is high and the tapered portion can be reduced.

Next, the reason why the method of the present invention is excellent will be described. 4 (a) and 4 (b) are action diagrams of the short side mold according to the present invention. FIG. 4 (a) shows the short side mold 2 at the time of starting or completing the width change, and forcibly cooled by the water-cooled mold 2. Thus, a solidified shell layer 8 is formed. The solidified shell layer 8 becomes thicker downward starting from the meniscus (free metal surface) 9, and the thickness of the solidified shell layer 8 is generally expressed by the following equation.

[0015]

(Equation 1)

That is, it grows largely in the initial stage, and thereafter grows gradually. In this case, the contact resistance of the lower end 2a of the short side mold 2 (the force with which the solidified shell layer presses the short side mold) is maximized. Further, a gap called an air gap 11 is generated between the casting surface 2b of the short side mold 2 and the solidified shell layer 8, and the air gap 11 may hinder the cooling operation.

FIG. 2B is a view in the middle of changing the width (see FIG. 2C). The upper side of the short side mold 2 is advanced with respect to the central part and the lower part, and the short side mold 2 is bent into a substantially “C” shape. As a result, the relatively large air gap 11 having both ends of the meniscus and the lower end 2a of the short side mold 2 in (a) is divided into two relatively small air gaps 12 and 13. The cooling effect has been greatly improved. Moreover, short side mold 2
Since the inclination of the central part and the lower part of (a) does not change from (a), the contact resistance at this part does not change from (a). Therefore,
The cooling action is improved and the contact resistance does not increase. If the contact resistance does not increase, there is no problem of peeling of the plating.

FIGS. 5 (a) to 5 (e) are views showing the movement of the short side mold (from narrow width to wide width) according to the method of the present invention, in which the moving speed of the upper cylinder 3 is V1 and the moving speed of the central cylinder 4 is V1. V
2, and in order to change the moving speed of the lower cylinder 5 to V3 and change the short side mold 2 from narrow to wide, first, V2 = V
3. The short side mold 2 of (a) is advanced in the direction of the arrow under the condition of V2 <V1. In (b), since the upper part of the short side mold 2 precedes the center part and the lower part, it curves forward by α,
Further, in (c) corresponding to the movement middle point, the upper part is β
(Where α <β). From (c), V2 = V
3. Change the condition to V1 <V2. That is, since the upper portion is slower than the central portion and the lower portion, the curvature of the upper portion returns to substantially α in (d), and the curvature is eliminated in (e), and the shape becomes the same as that of (a).

As described with reference to FIG. 4A, the solidified shell layer 8 immediately below the meniscus is still thin and easily deformed. Therefore, FIG.
In the manner of (a) to (c), the upper part of the short side mold 2 is advanced to deform the solidified shell layer 9, and the lower part of the short side mold 2 is followed.

In this embodiment, three short side molds 2 (3
The cylinder was moved and deformed by the cylinders 3, 4 and 5 in (stage). However, the invention is not limited to this, and the number of cylinders may be increased to four or more. In short, the cylinder moves the short side mold 2 during the movement. A minimum of three wires are required because they are curved
If the number is more than the number, the curve becomes smooth.

[0021]

According to the present invention, the following effects are exhibited by the above configuration. In the slab width changing method according to claim 1, the lower part of the short side mold moves at a predetermined speed, and the upper part of the short side mold has a first half of movement larger than the predetermined speed and 130 mm / mi.
n moves at a high speed with the limit as a limit , moves the latter half of the movement at a speed lower than the predetermined speed, matches the short side mold shape after the movement with the short side mold shape before the movement, during the movement of the mold
The upper part of the short side mold is curved in aく shape, and the air gap is reduced and shortened by curving the upper part of the short side mold in the く shape while the mold is moving. Since the increase in the contact resistance at the lower end of the side mold is suppressed, there is no fear that the plating applied to the casting surface of the mold will be peeled off, and that the slab will have surface cracks and breakout (leakage).

[Brief description of the drawings]

FIG. 1 is a principle diagram of a width changing device according to the present invention.

FIG. 2 is a view showing the movement of the short side mold according to the method of the present invention (from a wide width to a narrow width).

FIG. 3 is a graph showing the occurrence of molten metal leaks and cracks in the method of the present invention and the conventional method.

FIG. 4 is an operation diagram of the short side mold according to the present invention.

FIG. 5 is a view showing the movement of the short side mold according to the method of the present invention (from narrow width to wide width).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Width changing device, 2 ... Short side mold, 2a ... Lower end, 2b ... Casting surface, 3 ... Upper cylinder, 4 ... Central cylinder, 5 ... Lower cylinder, 6 ... Control part, 7 ... Line connecting upper and lower parts , 8
... solidified shell layer, 9 ... meniscus, 11 ... air gap.

Claims (1)

(57) [Claims] In a slab width changing method for changing the width of a slab from a wide width to a narrow width or from a narrow width to a wide width without interrupting a pouring operation, a short side mold is formed so as to satisfy the following conditions at the same time. A method for changing a slab width in a continuous casting facility, characterized by moving. The lower part of the short side mold moves at a predetermined speed. The upper part of the short side mold moves at a high speed higher than the predetermined speed and up to 130 mm / min in the first half of the movement, and moves at a lower speed than the predetermined speed in the latter half of the movement. The short-side mold shape after the movement is matched with the short-side mold shape before the movement. While the mold is moving, the short side mold becomes
Curve the top of the