JPS61266166A - Method for changing ingot width - Google Patents

Abstract

PURPOSE:To make possible the change of a billet width in the shortest time by determining the speed up rate of the horizontal moving speed on the short sides of a casting mold and the angular speed of a swiveling device by a prescribed method and maintaining constant these speeds during the former and latter periods of the movement of the short sides thereby changing the width. CONSTITUTION:The speed up rate alphas of the horizontal moving speed of the short sides is preliminarily determined with the permissible deformation resistance of a shell as a parameter in the stage of changing the width of the steel ingot by a short side driving device. The angular speed omega of the short side swiveling device is determined by the equation omega=alphas/Uc (where Uc: casting speed). The horizontal moving speed Vh is increased or decreased at the specified speed up rate alphas and the angular speed omega is maintained constant, then the width is reduced (a) or expanded (b) to the desired size in the former tilting period and latter tilting period of the short sides in the stage of changing the billet width. The change of the ingot width in the shortest time during continuous casting is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for continuous casting of steel, and more particularly to a method for changing the width of a slab by moving the short side of the mold during continuous casting.

[Conventional technology]

In recent years, in continuous casting, especially continuous casting of steel, continuous casting methods, which change the slab width without stopping pouring into the mold, have been developed due to demands for improved operating efficiency and slab yield. It is starting to be implemented.

In particular, recently, a method of combining the continuous casting process and the rolling process into 11 blocks has been put into practical use, and the technology of changing the width of the slab during continuous casting according to the width of the product sheet is becoming increasingly important. When changing the slab width without interrupting the operation of the continuous casting machine, it is important to keep the length of the portion where the width changes as short as possible and to immediately change the width to the required width. For this reason, it has become necessary to increase the width change speed.

To change the width of a slab in continuous casting, the short side of the mold is moved toward the center or away from the center of the mold by some method. FIG. 2 conceptually shows an example of a width changing device that fixes the long sides of the mold and moves the short sides. A pair of short sides 1a and lb are held between long sides 2a and 2b fixed to a mold vibration table (not shown), and are driven horizontally by a drive device (not shown). This device changes the width of the slab 4 without stopping casting. When increasing the speed of width change in such equipment, there is an increase in the force driving the short side and an increased risk of slab defects, which has hindered the speed of width change.

As a conventional width changing method, for example, Japanese Patent Publication No. 56-491
As shown in Publication No. 73, this was done by a single spindle connected to the back of the short side and movable in the horizontal direction, and swingable by the rotation of a cam mechanism using a spherical seat as a fulcrum. . That is, although the spindle can perform horizontal movement and rotational movement at the same time,
When actually changing the width, it is common to use a cam mechanism to tilt the short side to a predetermined angle, then maintain that state and move the short side in parallel, and the width change speed is extremely slow. Met.

On the other hand, as disclosed in, for example, Japanese Unexamined Patent Publication No. 53-60326 and Japanese Patent Publication No. 54-33772, two electric or hydraulic drive devices are installed in the vertical direction of the short side, and Attempts to change the width at high speed by controlling each of the two drive devices are also being actively adopted.

3 and 4 show an example of a specific method of controlling the two upper and lower drive devices to change the width, and FIG. 3 explains the case of width reduction. IJ),
In the first step shown in (a), the short side 1 is tilted as shown by the dotted line a, and in the second step, after being translated in parallel as shown in (b),
Next, in the third step, as shown in (C), a method of returning the slope to its original state is shown, and in Fig. 4, the case of widening the width is explained. This figure shows a method of tilting as shown in (a), moving in parallel as shown in (b) in the second step, and then reducing the inclination as shown in (c) in the third step.

In other words, in all of the above-mentioned conventional art, the taper change operation and the parallel movement operation were performed completely separately.

However, in the conventional method, in order to increase the width change speed, it is necessary to increase the parallel movement speed Vm'z. However, in order to increase the parallel movement speed Vm'z without breaking the shell solidified in the mold and by overcoming the deformation resistance of this shell, the angle of change in inclination Δφ must be increased. There is a problem.

On the other hand, when the inclination change angle Δφ is increased, a gap, that is, an air gap, is created between the short side 1 and the slab 4, and when this air gap becomes large, cracks may occur in the slab 4,
There are problems such as breakouts occurring.

For this reason, in the conventional method, there is a limit to increasing the parallel movement speed Vm, and there is a limit to reducing the width changing time completely. In order to solve all of these problems, the present applicant developed a method in which the lower end of the short side is simultaneously moved to the - side in the first and third steps to shorten the time required for this period. -73155 and JP-A-60-33855. However, even in this method, the basic idea is to perform parallel movement, and although it is advisable to make the time to reach parallel movement as fast as possible, it is still possible to shorten the total time required to change the width. had its limits.

[Problem that the invention seeks to solve]

The present invention fundamentally solves the problems in the conventional methods described above, and further improves the above-mentioned Japanese Patent Application Laid-Open Nos. 59-73155 and 60-33855. In a mold equipped with a swing drive device that operates independently from the cast iron, the width can be changed by increasing or decreasing the slab width by 1 to 10 degrees in the minimum amount of time during continuous casting, thereby reducing the number of width changes and increasing yield. The purpose of the present invention is to provide a method that improves the casting process and enables stable operation without occurrence of casting defects such as breakout (hereinafter referred to as BO) and cracking of slabs.

[Means for solving problems]

The structure of the present invention intended to solve the above problems will be explained below.

First, an example of the short side drive device applied to the present invention will be described in the fifth section.
This will be explained based on the diagram. In FIG. 5, 1 indicates the short side of the mold, and a bearing part 12 is fixed to the back of this short side 1, which supports a rotating shaft 11 perpendicular to the casting direction X and the horizontal movement direction y of the short side 1. ing. A horizontal drive device w (hereinafter referred to as a drive device) 13 is connected to the rotation shaft 11 . A rotating arm 120 is provided protruding from the bearing portion 12.
A swing drive device ft (hereinafter referred to as a swing device) 14 that is placed on the horizontal drive device 13 and operates independently of the horizontal drive device 13 is connected to this swing arm 120. .

Therefore, by driving the drive device 13 back and forth, the short side 1 is moved in the horizontal direction. Further, by driving the turning device 14, the short side 1 turns around the turning shaft 11 as a fulcrum. Therefore, when changing the width, it is effective to position the rotating shaft 11 near the center of gravity of the total reaction force acting on the short side 1, since the turning force of the turning device 14 can be reduced. Generally, the position of the center of gravity is determined by the ratio C11/ of the distance t1 from the level equivalent to the meniscus to the rotation axis 11 and the distance t2 from the rotation axis 11 to the lower end of the short side, as shown in FIG. 8, which will be described later. 12) but 2~
It is in the range of 5. Of course, if there is sufficient turning force of the turning device 14 or depending on the arrangement of equipment near the short side, the position of the rotating shaft 11 may be approximately at the center of the short side 1, or the position of the rotating shaft 11 may be adjusted to the casting direction. It is also possible to set it to the position of Renhui in . The front N[4-time movement edge movement can be performed independently by moving the short side l in the horizontal direction (hereinafter referred to as horizontal movement).

In other words, it is possible to perform a rotation operation while horizontally moving the short side, and of course stopping the horizontal movement.
Rotation operations can be performed even in the closed state.

In the present invention, the Af, IR horizontal drive device 13 and the swing drive device 14 will be collectively referred to as the short side drive device hereinafter.

Now, when changing the slab width during continuous casting using a mold equipped with the short side drive device, in the present invention, the movement of the short side (horizontal movement and rotation of the short side are collectively referred to as The horizontal movement direction of the short side in each period is divided into a forward tilting period in which the short side is sequentially tilted toward the center of the mold, and a backward tilting period in which the short side is tilted toward the center of the mold. The speed increase rate αs
is determined in advance using the measured shell deformation resistance force as a parameter, and the angular velocity ω of the swing device is determined by the equation 11 below. It is characterized by the fact that

ω=αs/Uc・・・・・・(
1) However, ω: Angular velocity of the turning device (rad/min) α
s: Acceleration rate of the horizontal movement speed of the short side (dish speed n2) LJc: Casting speed 13j (mm/min) In the width changing method, the rolling conditions and/or the constraints of the short side drive device Maximum allowable horizontal movement speed of short side Vm
ax is set, and when the horizontal movement speed of the short side in the forward tilt period of the first half of the width change or the rear cheek exceeds the above Vmax, the following (2) and (
The short side is translated in parallel at a translation speed Vp within the range expressed by equation 3), making it possible to change the width in the shortest possible time while preventing casting defects.

l Vmax I≧IVpl ・・・・・・ (
2) 'Vp≧αsl ・Tri = (3) However, Vmax", maximum allowable horizontal movement speed (mm/min
) vp; parallel movement speed (mm/min) asH
Acceleration rate (mm/1nln2) of the horizontal movement speed of the short side of the anteversion phase or rear cheek area in the first half of width change Trl: Required time for the anteversion phase or ridge cheek area in the first half of width change Further, in the width change method, The error in the target width change amount resulting from the difference between the taper amount at the start of the width change and the target taper amount at the end of the width change is calculated by adjusting the error between the anteversion phase and the rear cheek area, or the transition from the rear cheek area to the anteversion phase. It is preferable to absorb it by providing a moving period.

[For production]

FIG. 1 explains the basic width changing method based on the present invention, and is a diagram illustrating the horizontal movement speed and rotation speed of the short side when changing the width. Figure 1 (,) shows the width reduction,
FIG. 1(b) shows the width expansion, and the horizontal movement speed is expressed as positive (plus) when moving toward the center of the mold, and negative (minus) when moving toward the side away from the center of the mold. The rotation speed is expressed by the angular velocity ω of the rotation device, and the direction in which the inclination angle β increases as shown in FIG. Tilt angle β is small
□The direction in which it becomes thinner, that is, the direction in which the short side is tilted away from the center of the mold, is expressed as a negative (minus).

First, the case of width reduction will be explained based on FIG. 1(3).

In the figure, the solid line a represents the horizontal movement speed vh of the short side, and the solid line a represents the angular velocity ω of the turning device. To reduce the width, the short side is moved toward the center of the mold, but in the first half, the short side is tilted forward toward the center of the mold, and when approximately half of the target width change amount is reached, no parallel movement is performed. Immediately perform a backward tilting operation to tilt the short side away from the center of the mold to complete a series of width changing operations. FIG. 6 is a schematic diagram showing the movement of the short side when the width is reduced.

The horizontal movement speed vh of the short side during the width changing operation is:
A constant acceleration rate αs1, that is, forward tilt, in the front and rear cheeks (the period in which the forward tilting operation is performed in 1 is called the forward tilt period, and the period in which the backward tilting operation is performed is called the rear cheek region, and these are collectively referred to as the front and rear cheeks). In the period, the speed increasing rate αl increases in the positive direction, that is, toward the center of the mold, and in the rear cheek region, the speed increasing rate α−[positive direction decreases the moving speed toward the center of the mold. If this is used as a standard, it will be the deceleration rate, but in the present invention, it will be used uniformly as the speed increase rate, and if it is necessary to express it separately, the sign will be used to express the speed increase with (+) and the deceleration with (-). do. In addition, when this is referred to generically, it will be referred to as the acceleration rate α- below. ], each of which increases or decreases over time. As will be described later, the speed increase rate αs is determined in advance using the allowable shell deformation resistance as a parameter.

10,000, the short side in the forward tilting phase is controlled to rotate at a constant angular velocity ω in the positive direction determined by the equation (1) above based on the casting speed during the operation and the speed increase rate α$, and 6
Inclination angle β of short side 1 with respect to horizontal line 2 shown by the dashed line in the figure
gradually increases, and the forward tilt gradually increases. On the other hand, in the rear cheek, the short side rotates at a constant angular velocity ω in the negative direction.
The inclination angle I gradually decreases, and the amount of forward inclination decreases.

Therefore, in Fig. 1, the acceleration rate in the forward tilt phase is αml
, the angular velocity is ω1, and the acceleration rate at the rear cheek is αm2
, the angular velocity was manipulated by ω2, the time to turn from the anteversion period to the rear cheek area was shown as Tr, and the total time required to change the width was shown as Tw.

Next, the case of width expansion '1 will be explained based on the schematic diagrams of FIG. 1(b) and FIG. 7. In carrying out width expansion, the short side is moved toward the mold and center direction, contrary to the aforementioned width reduction, but first, in the first half, a constant angular velocity ω in the negative direction is applied.
While rotating the short side with , tilt backward and move at a horizontal movement speed with a constant acceleration rate αs + f as described in I ~ above, and after moving the foot scene, immediately switch to the angular velocity in the positive direction. Perform forward leaning maneuver. Even in this forward/backward tilting operation for widening the width, the horizontal movement speed of the short side has an acceleration rate αbf, and is accelerated or decelerated with time. In addition, in Fig. 1 above, the first half of the width change (the anteversion period when the width is reduced, the ridge period when the width is expanded) to the half part (the rear cheek part when the width is reduced, the anteversion period when the width is expanded) ) The reason for the deviation in the horizontal movement speed V 11 when shifting to ) is that the rotation fulcrum on the short side deviates from its center position as shown in Fig. 8 (C11>12), which will be described later. When the pivot point is located approximately at the center of the short side (11=12), the above-mentioned deviation does not occur, and the horizontal movement speed Vb at the end of the first half is equal to This is the horizontal movement speed vh at the start of the 7-keke forward leaning phase.

As described above, in the present invention, the speed increase rate αs is determined and set in advance according to the steel type, slab size, manufacturing speed, etc. using the metering shell deformation resistance as a parameter, as will be described later, and the angular velocity ω of the turning device is By determining the width based on the above formula (1) and changing the width while keeping it constant during each period of the forward leaning period and the rear cheek area, we succeeded in achieving the great effect of the glaze as described below. It is something. .

Now, the reason why the width change of the present invention can be efficiently implemented by using the above-mentioned speed increase rate α and angular velocity ω as control factors will be explained.

As mentioned above, in order to increase the speed when changing the width, it is necessary to take care not to cause defects in the BO' or slab during the width change. For this purpose, it is necessary to avoid creating an air gap between the slab and the short side during the entire width change implementation period.
In addition, it is important to always ensure proper pushing so that the slab is not pushed in excessively by the short pieces.

FIG. 8 is a configuration diagram illustrating the relative movement of the slab and the short side when the short side is moved during continuous casting using the short side drive device shown in FIG. 5. First, the strain that occurs in the slab when changing the width will be explained based on FIG. 8. In addition, in Fig. 8, this is the part corresponding to the meniscus on the short side by 1u, and 1
t is the lower end of the short side, β is the inclination angle between the short side and horizontal line 2, and θ is the inclination angle with respect to the vertical line (θ = β - 90'
).

At time t, short side 1 is at position B1, and when it moves to position B2 during the elapse of minute time dt, it is tentatively added. The horizontal movement speed during this minute time diO is 1vh, and the angular velocity is ω. Also, during the minute time diO, the short side meniscus equivalent part 1u is dYu, and the short side lower end 1tiI-j: dYt.
,Moving. At this time, the slab 4u that was in the meniscus equivalent portion 1u at time t moves to 4ul after a time di, and the slab 4t that was in the lower end 1t of the short side moves to 411. This moving distance is [Uc·at].

As the short side moves from B1 to B2, the appearance of the slab is upward, dYu at the meniscus equivalent, and dYL at the lower end of the short side.
However, as mentioned above, the slab is actually pushed in [Ucs
dt) and downward, the deformation by the horizontal displacement [Uc@dLefanθ] due to this movement is alleviated. Therefore, if the amount of deformation that the slab actually undergoes is ηu1 at the meniscus equivalent part, and ηt at the lower end of the short side, then ηU and ηt
is given by the following equations (4) and (5).

dηu=dYu−Uc * dt @tanθ
......(4) dηL=dYL-Uc*dt
@tanθ ・・・・・・(5) On the other hand, let the horizontal displacement of the short side be X, and let the inclination angle of the short side be dθ between di
If it is assumed to be displaced, dYu and dYL can be expressed by the following equations (6) and (7).

dYu=tl ・tan(θ+dθ)+ctx−tl
11tanθ・(6)dYL−−12IIjan(a+
d) + dX −(-22・tanθ)・(7) However, t
l; Distance t2 from the meniscus equivalent part 1u to the drive device (rotation shaft 11 in FIG. 5); Distance from the lower end 1t of the short side to the drive device (rotation shaft 1 in FIG. 5)
Since the distance θ to 1) is small, the following approximate equation holds true.

Electric anθ equal θ (8) Substituting the above equation (8) into the above (6) and (7), the following (9) and (1o) are obtained.
Formulas are obtained, and formulas (8) to (10) are further converted to formulas (4) and (
By substituting into formula 51, we get the following (1s, (12)
A formula is required.

dYu=t1sdθ+dx ・・---(
9) dYt=-12・dθ+dX...
...(10) dηu=tl・dθ+dX−Uc*dt・
θ−(11)dηt=−12”dθ+dX−Uc@dt
sθ・(12) By dividing the equations (11) and (12) by di, the following equations (13) and (14) can be obtained.

dηu/d t=l u=tI IIdθ/dt+dX
/a t-Uceθ・<13) dvt/dt=iL=-
12@dθ/dt+dX/dt-Uc ・θ=(14)
Here, d Ij u / d t-'7 u %dη
t/dt=;yL represents the actual amount of deformation per unit time, that is, the deformation speed. Further, dθ/at represents the time change in the inclination angle of the short side, that is, the angular velocity ω. Furthermore, dX/dt represents the temporal change in the horizontal displacement of the short side, that is, the horizontal movement speed vh.

Next, the strain in the slab can be determined by dividing the amount of deformation of the slab by the length at which deformation occurs, that is, half the width of the slab.

That is, when the above equations (13) and (14) are divided by the half wave W of the slab width 2W, the strain rate is obtained by the following equations (15) and (16).

111-tl・ω/W+V h /W−U c・θ/
W ・・・・・・(15)Go1=-12・07w +
V h /W −U c skewer θ/W (16)
In order not to change the strain rate over time, that is, to keep the deformation of the slab always appropriate, [d 2 u/d t=o
:), [aAt/at=o] is sufficient. Therefore, it is only necessary that the following conditions (17) and (18) be satisfied.

aiu/dt=(tl/W)φdω/dt+(1/W)
・dvh, /dt-(Uc/W)-ωmi0...
...(17) a Qt/d t=(-t2/W)
・aω/a t+(1/W) 11dVh/a t-(
U c/W) ・ω=O・・・(18)(17)
, the following equation (19) can be found from equation (18).

dω/dt=o (19
) (19) gives the following equation (20), and (19)
) is substituted into the above equations (17) and (18), the following equation (21) is obtained.

ω=β ・・・・・・(20) However, β: Integral constant dVh/dt=Uc”ω ・・・・・・(21) Since the right side of the above equation (20) is constant with respect to time, In the case of a person, it is expressed as equation (22).

dVh/dt=Uc''ωmiA (22) By solving equation (22), the general solution can be found as shown in (23) below.

Vh=A-1+r -=・ (23) However
γ: Integral constant Also, from the above equation (22), the following (s') can be found.

ω=A/Uc...(1)'
□In other words, according to equations (23) and (1) 1, in order to keep the deformation of the slab always appropriate without changing the strain rate over time as described above, start changing the width of the horizontal movement speed vh of the short side. New knowledge has been obtained that it is sufficient to set the angular velocity ω as a linear function of the elapsed time t from the time t and that the angular velocity ω is always kept at a constant value determined from A and the slab velocity Uc.

Based on this knowledge, the present inventors conducted further research on width changes during continuous casting in actual operations, and found that ml (2
It was confirmed that the above knowledge could be applied on an industrial scale by setting the constant A in formulas 3) and (])' to a value determined using the allowable deformation resistance as a parameter.

In the present invention, the constant value has a value other than zero, and therefore the horizontal movement speed yh is increased or decelerated with time. In the present invention, a constant A for accelerating or decelerating vh during this width change period is used as the accelerating rate α. Further, the integral constant r in the above equations (23) and (1)' is the initial speed at the start of the horizontal movement speed vhO width change, and may be appropriately determined in advance depending on the width change and the operating conditions at that time.

When the speed increase rate αs is set, the angular velocity ω is determined from the casting speed Uc during the operation as ω=αs/Uc (1), and the above-mentioned equation (1) is obtained.

Next, a specific width changing method based on the present invention will be explained.

As mentioned above, in order to keep the strain generated in the slab constant during width change, it is found that it is sufficient to keep the acceleration rate αs of the horizontal movement speed vh and the angular velocity ω constant, and the angular velocity at that time is ω is determined from the speed increase rate αs and slab speed Uc using the above equation (1). Therefore, if α field is positive, ω will also be positive, and the short side will tilt forward. Conversely, if α$ is negative, ω will also be negative, and the short side will tilt backward.

At the end of the width change, it is necessary to restore the inclination angle of the short side to almost the same level as at the beginning of the width change, so in order to perform a series of width changes, the period in which αs is positive or negative must be set at least 1 or more, respectively.
I need. Various width changes are possible by combining the positive and negative periods of αs, but the simplest and fastest speed is when αs is configured with one positive and one negative period, as shown in Figure 1. This is the case. This is a case where the entire period of hip width change is divided into the anteversion period and the rear cheek area.

Therefore, if the horizontal movement speed vh and angular velocity ω of the first half and the second half of the width change are expressed with subscripts (1 means the first half, 2 means the second half), they can be placed as follows.

First half Vhl-αs1・t+γ1...(24)ω
1-αml/IJc --(25)
Second half V h 2 = αs2 ・t + r'2 ”=
= (26)ω2-αs2/Uc
--<27) (24) Machine 27) is converted into the above (15), (
Substituting into equation 16), the strain rate for each period is as follows (28) ~
It can be found as in equation (31).

First half k u 1 = (11/W) - (α82/UC) + r
l/W ・−・・−・(2s>2t]=(−t2/
W)・(α82/UC)+γ1/W...(29) (αm2/Uc)+γ2/ of the second half i u 2-(tl/W)
/w−αsl ・Tr/W・−・(30)tt2=(−
t2/W door (αs 2/Uc) + γ2/%'l'-C
1 m 1 ・T rlfJ"< 31) However, if the strain rate becomes negative, an air gap will be created, and if it exceeds this value, the driving force of the short side 1ife moving device will increase significantly, and the slab 75 (seating A bending phenomenon occurs, making stable casting impossible.The strain rate 2 in equations (28) to (31) above must satisfy the following conditions.

0≦Second eye≦2maxi (32) However, i: Short side meniscus equivalent part u1 or lower end tj; First half of width change, or second half Therefore, according to formulas (28) to (30) When formula (32) is substituted, the following (33) to (36) hold true.

O≦(tllW) ' (αml/Uc)+H/W≦i
max u −= (33) 0≦(-12/W)”
(α82/UC)+rl/W≦imax L...(3
4) 0≦(tlzroichi/)-(α82/UC)+γ2/
'W-αml@Tr/■≦imaxu'' (3r)0≦
(-t2/W)・(αm2/Uc)+γ2/w−αs1
・Tr/'W≦imax L, -<36) The following formulas (,) to (h) can be found by arranging the correlations to satisfy the above formulas, that is, to maintain stable casting during width change. .

r1≧−11−Cαs1/Uc)
"・"・(a) γ1≦W(2max u-(t1/W)
・(αsl/Uc))=−41−(αsl/Uc)+
W112maxu +-+-(1)) r1≧12
−(αs 1 /U c )・”=・
(c) γ1≦12−Cαs 1/Uc ) +W・6
max L-・” (d) γ2〉α5lsTr-61・
(αs2/Uc)----"(e) γ2≦-t1"
(αs 2/U c ) 10αsl・Tr+W'2max
u ” (f) γ2〉αs1・Tr+t2・(6m
2/U c ) −・” (g) r2≦12−C
αs 2/U c )+αa 1 ・Tr+W @i
max L ・=(h) Figure 9 shows these (a) to (h)
9A shows the first half and FIG. 9 shows the second half. Further, the horizontal axis shows the speed increase rates αsl and αs2, and the vertical axis shows the initial speeds γ1 and γ2. The hatched portion in FIG. 9 indicates a range in which no casting defects occur, that is, a range in which the width can be changed while stable casting is continued. Therefore, by selecting and setting the speed increase rates αsl, αs2 and the initial speeds γ1, γ2 to arbitrary values within the ranges of the hatched portions, the above-mentioned width change of the present invention can be implemented.

By the way, as mentioned above, the width change is required to be carried out as quickly as possible, and it is necessary to find the speed increase rate αs that satisfies this requirement from within the range of /% latching l). . In the first half of the width reduction, the speed increase rate αs is positive, and the larger its absolute value, the better. From this, the point P1 shown in FIG. 9a becomes the optimal condition. or,
In the first half of width expansion, the speed increase rate αs is negative, and the larger its absolute value, the better. Therefore, point P3 is optimal.

Next, in the second half of the width change, the inclination angle that was tilted more than during normal operation in the first half must be returned to its original value, so ω1eTr==-ω2・(TW-Tr)...
・(37) ω1=αs l / U c sω2=αs
Since 2/UC, Tw-Tr=-(αsl/αm2)
-Tr...'' (: U8), and in order to reduce the width change time, the larger the absolute value of αs2 is, the better. In the case of width reduction, the point P2 shown in Figure 9 is
In addition, in the case of width expansion, point P4 shown in FIG. 91 becomes the optimum point.

As described above, the speed increase rate α is determined in order to minimize the width change time, and Table 1 below shows it as a list.

1. On the surface, the horizontal movement velocity vh and angular velocity change ω under the conditions shown in Table 1 of Senki are as shown in Table 2 (width reduction) and Table 3 (width expansion) below.

Table 2 Table 3 In addition, in the experience of the present inventors, the shell thickness is thinner above the short side than below, so generally 2max u) 2max t...
(39), □In the case of width reduction, 1αall, >lα@21...(40) In the case of width expansion, l αil l < I (Xs21...
- (41) is possible from the shell deformation resistance and is effective from the viewpoint of increasing the width change speed.

On the other hand, when it comes to αs well α2, there is a transition from the anteversion phase to the cheek area,
In other words, control of the turning point becomes complicated. Therefore, when ease of controllability is important, it is preferable to set αsl=αs2. In any case, αs1 and αs2 can be arbitrarily set within the above range depending on equipment conditions, operating conditions at that time, etc.

Next, a specific method for determining the speed increase rate αs will be explained.

As mentioned above, the speed increase rate α$ can be determined from the strain allowed for deformation of the shell, but for example, if the present invention is implemented using an existing short side drive device, or if there are restrictions such as the installation location or equipment cost. If there is a limit to increasing the capability of the short-side drive device, the width αs determined from the above-mentioned allowable strain of the shell may not be sufficient to change the width.

In such a case, it is possible to find a speed increase rate αs that is within the above-mentioned shell strength and that allows the short side drive device to efficiently demonstrate its capabilities.

By the way, the inventors conducted tests with various acceleration rates α and initial speed r, and found that the total driving force F required for rounding the short side horizontally can be calculated using the following equation (42). confirmed.

F = 2 S LH + LHn 511nH,;,,
(smell) dsdE ・・・・・・(42) Here E
represents the distance on coordinates where the meniscus equivalent part on the short side is set to "0" and the casting direction is set as positive. Moreover, i<w> is determined by the following equation (43).

2(Fi)-((LL-iu)/(L1+t2)
) ・Fl+ Au... (43) U%il is the above (
28) ~ (calculated by formula 30, αml, α$2 and rl
, r2 can be determined.

Furthermore, H is the shell thickness, which can be calculated using the following equation (44).<SO is the creep constant, which is given by the following equation (45).

H= Ho’s (E/U c ) 1/2・” −
(44) G=Go @e x p (q/Re)
-(45) In the formula (44), Ho is the solidification coefficient, which is usually 18 to 25 mm/r111n in the case of ordinary steel.
It is within the range of 1/2, and strictly speaking, it is determined by measuring the shell thickness for each steel type. (42), (45
) Go, n in the formula.

q is a coefficient determined from the physical properties of the target steel type, and can be determined by conducting a tensile test for each steel type. ne is the temperature (0K).

By sequentially changing the speed increase rate αs and the initial speed γ as described above, E(1, λt is obtained from the above equations (28) to (31), and by substituting it into e (43) equation, the total assembly force is calculated. F is calculated.

On the other hand, the ability Fav of the short side drive device to effectively act on the deformation of the slab through the short side is calculated by calculating the static pressure Pg of the molten steel and the sliding friction force Fμ from the generation ability Fa as shown in equation (46) below. The value will be reduced.

Fav = Fa - Fg - Fμ - (46) Therefore, the width change pattern is determined by setting the speed increase rate αs and initial velocity r so as to satisfy Fav)F, and determining the angular velocity ω based on it. Ru.

By the way, in the example shown in FIG. 1, the horizontal movement speed of the upper and lower ends of the short side increases with time, and if there is a limit to the horizontal movement speed due to constraints such as the short side drive device as described later,
It is not possible to secure the entire required width change amount with one width change operation. To solve this problem, it is necessary to increase the capacity of the short side drive device, modify the drive mechanism, or repeat the width changing operation. In the present invention, this problem can be solved by changing the forward leaning period (width reduction) in the first half of the width change from 1 to 1 or the rear cheek part (width expansion) to the rear cheek part (width reduction) or forward tilting in the latter half of the width change. This can be effectively solved by moving the short side in parallel during the transition to the phase (width expansion).

That is, from equations (23) and (1) above, in order to keep the deformation of the slab always appropriate during the width change period, it is necessary that the horizontal movement speed vh is a linear function of time t and that the angular velocity ω is constant. However, even in the case of (λ-α$=0) in equations (23) and (1), the equations (19) and (
22) formula is satisfied.

In this case, the angular velocity ω also becomes (ω-0) from equation (1),
The short side moves in parallel. In other words, even when this parallel movement is performed, it is possible to maintain the deformation of the slab at a constant target value.

Therefore, as a result of further research, the inventors of the present invention have divided the width change method of the present invention into the forward tilting period of the short side and the rear cheek area, and have determined that the horizontal movement speed of the short side in each period is The speed increase rate αs is determined in advance using the allowable shell deformation resistance force as a parameter, and the angular velocity ω of the swing device is determined by the (1
), and during the period, the speed increase rate αs and the angular velocity ω
In the width changing method in which the width is changed while maintaining the width constant, the maximum permissible horizontal movement speed Vmax of the short side is set based on the rolling conditions and/or the constraints of the short side drive device, and the forward tilting period of the first half of the width change is set. , or when the horizontal movement speed of the short side in the rear cheek exceeds the V max, the width is changed between the first half and the second half within the range shown in equations (2) and (3) above. It was confirmed that by moving the short side in parallel at speed VD, it was possible to change the width in the shortest possible time while preventing the occurrence of casting defects.

Now, in what cases the horizontal movement speed yh of the short side is limited will be explained. When the width is changed as described above, the slab produced during that time will be as shown in Figure 10 (a).
) with a tapered metal plate as shown. Conventionally, this slab with a taper when changing the width (hereinafter referred to as 4m width changing slab)
) is the ridge where the slab is layered or cooled, the first
1. Cut off a part of the taper as shown by the broken line in Figure 1(b),
A method of subsequently reheating and rolling was generally employed.

However, this method leads to a decrease in yield and a rise in energy costs, and it has therefore been desired to roll the width-changed slab into a product without cutting or other processing. In this case, there is a problem that if the taper t of the slab is increased too much, it cannot be rolled. Since the amount of taper of the slab is determined by the ratio of the forming speed and the width changing speed, if there is a limit to the taper amount, there is also a limit to the horizontal movement speed vh.

On the other hand, in the short-side drive device as shown in FIG. 5, there is a limit to the rotation angle ζ of the bearing, and there is also a limit to increasing the inclination angle β when changing the width. In the width changing method shown in FIG. 1, the inclination angle β increases or decreases with time, so if there is a limit to the inclination angle β, there will also be a limit to the time required for the anteversion phase or the rear cheek area. Therefore, the short side movement speed is limited.

In the present invention, when the above problem occurs, the maximum moving speed V max of the short side at the time of width change is set as described above, and when the horizontal moving speed vh of the short side in the first half of the width change exceeds the above V max, This problem can be effectively solved by performing parallel movement between the first half and the second half of the width change at a speed that satisfies a predetermined condition. FIG. 11 is a diagram illustrating the horizontal movement speed and rotation speed of the short side when changing the width based on the above method, in which FIG. 11(a) shows width reduction; This figure shows an enlarged view of C11 with the pivot point set at approximately the center of the short side.
+12) This is an example.

In the case of width reduction shown in Fig. 11(a), the short side is moved toward the center of the mold, but in the first half, the short side is moved until the horizontal movement speed vh reaches the maximum allowable movement speed max. Perform forward tilting operation to tilt toward the center of the mold. During this forward tilting period, while rotating at a positive angular velocity ω,
The forward tilting operation is performed with a constant speed increase rate αsf. Said V
When the angular velocity reaches max, the rotation device is stopped, the short side is moved at the parallel movement speed Vp, and after the parallel movement time determined by the target width change amount has elapsed, the angular velocity is switched to the negative direction ω, and the short side is moved at the parallel movement speed Vp. The operation is performed in the direction of the center of the mold, and a series of width changing operations is completed.

Next, when enlarging the width, the short side is moved toward the mold and the center, contrary to the width reduction described above, but in the first half, the short side is rotated at a constant angular velocity ω in the negative direction. As described above, the backward tilting and movement are performed at a horizontal movement speed with a constant acceleration rate α@, and when the V max is reached, the parallel movement is performed at a parallel movement speed vp, which is determined based on the target width change amount. Immediately after the parallel movement time Th elapses, the angular velocity is switched to the positive direction and the forward tilting operation is performed. Even in this front edge tilting operation for widening the width, the horizontal movement speed of the short side has an acceleration rate α8f, and is accelerated or decelerated with time.

Next, the method of setting the maximum moving speed V maxO of the short side will be explained.

As described above, the maximum moving speed V max of the short side may be set based on the subsequent rolling conditions or may be set based on the constraint conditions of the short side drive device. First, the case where rolling conditions are set will be explained.

As shown in FIG. 10, when the taper amount ξ of the slab increases, for example, an end induction heating device installed in a conveying device during feeding from a continuous casting machine to a rolling mill can achieve the desired end heating. or there may be an error in the width dimension of the product after rolling. Regarding the latter width error, a technology has been developed in which a width reduction device is installed in front of the rolling mill, but there is a limit to the amount that can be corrected by this width reduction device, and when the taper amount ξ exceeds a predetermined value, the width error Occurrence cannot be avoided. Therefore, the width of the cast slab 4aK is determined based on the taper amount allowed by each equipment installed after the continuous casting machine and the width error allowed for the rolled ridge product.
Determine the amount of taper ξ allowed by iFF. (In the present invention, the rolling conditions include the width accuracy due to the above-mentioned rolling, other rolling conditions as well as conditions permitted by each equipment installed in the process of conveying the slab from the continuous casting machine to the rolling machine. ) This taper amount ξ is expressed as the following equation (47) using the casting speed Uc and the horizontal movement speed vh, since the shape of the slab is determined by the width of the lower end of the mold. be.

ξ= V h / U c ・” (47
) Therefore, in order to make the taper t of the slab less than or equal to the predetermined ξ, the horizontal movement speed vh must be less than or equal to Vmax determined by the equation We (48) below.

Vmax=ξ·UC (48) Next, the case where it is set based on the constraint conditions of the short side drive device will be explained. As a constraint on the short-side drive device, there are times when a limit is placed on the rotation angle ζ of the bearing portion, and there are times when a limit is placed on the ability of the drive device. This restriction on the rotation angle arises from the structural reasons of the bearing part or the need to suppress the gap eFF between the long side and the short side in curved molds, etc., and determines the maximum possible rotation angle ζmax. The rotation angle ζ is expressed by the degree of inclination, and in the width changing method shown in FIG. 1, ζ = ω・
t...(49). At this time, since the horizontal movement speed in the first half of the width change is vh ke vh - αsl ・t 0rl ... (50), ■ h - U c fist ζ + γ ] −
It can be expressed as -----・ (Flu). Therefore, Vmax is determined by the following equation (52).

V max = U c * ζ max + γ1 ・(52
) Also, if a restriction is imposed by the cylinder capacity of the drive device, the maximum speed of the cylinder will be V max.

As described above, the maximum speed V max of the short side is set based on the rolling conditions, the constraint conditions of the short side drive device, or both. In the width changing method shown in FIG. 1, the horizontal movement speed h of the short side reaches its maximum at the turning time Tr. If the maximum horizontal movement speed at this time is V h max, this V h max is manipulated by the following equation (53).

V h max-α81・Tr+γ1 −・・−・
- (53) In the present invention, when the V h max exceeds the V max, the short side is moved in parallel without exceeding V max and at a speed higher than the speed described later.

Now, the parallel movement speed Vp needs to be set so that the parallel movement can be performed while maintaining conditions in which no air gap is generated in the first half of the width change and no excessive pushing is caused.

The strain rate of the slab during the parallel movement period at both the upper and lower ends of the short side is calculated from equations (15) and (16) above as shown below (
54) is expressed by the formula.

'/ u = '7 t = (Vp/W) (Uc
/W) ・ω*Trl= (Vp−αs1・Trl)
(54) If 1u and 11 are less than zero, an air gap will be created between the slab and the short side, resulting in casting defects.

Therefore;) t+, t must be positive.

From this, the parallel movement speed Vp can be calculated using the above equation (54) and V
Based on the condition that it is less than or equal to max, the following formula, that is, the above-mentioned (2)
and (3).

I V max l≧1Vpl (2
)Vp≧αs1@Tr (3) The above-mentioned restriction on the horizontal movement speed of the short side limits the magnitude of the absolute value of the speed, so the above equation (2) is expressed as the absolute value. It is necessary to display it with money.

Now, as is well known, the inclination angle of the short side during normal operation is set by the slab width, casting speed, etc., and the wider the slab width, the more the taper -i! : <In the present invention, the taper amount refers to the horizontal distance between the upper end and the vertical line Yz passing through the lower end of the mold shown by the two-dot chain line in FIG. 6, and the inclination angle β is 90
When the taper is 1°, the taper l' is ±0. The taper amount is hereinafter expressed in terms of dew. ) becomes larger, and as the slab width becomes narrower, the tapered leaves also become smaller.

Therefore, if the width of the slab is changed during continuous casting, the width of the slab will change before and after the change, so the inclination angle β of the short side will also change, and it is necessary to change the taper amount as well. be. For example, if this taper amount change is performed after the width change is completed, an operation to change only the taper amount (hereinafter referred to as the taper amount correction operation) must be performed separately from the width change operation, which causes the following problems. In other words, controlling the width change is very complicated and troublesome, and casting is performed with an inappropriate taper amount from the end of the width change until the end of the taper amount correction operation, resulting in slab defects. In addition, if the lower end of the mold or the upper and lower ends of the mold are simultaneously moved in the taper I correction operation and the taper I'e is corrected, the amount of width change of the slab and the actual width change will be different. There is a very high possibility that the width of the slab will be incorrect.

On the other hand, the rear cheek area corresponds to the latter half of the width change based on the present invention,
Alternatively, a method may be considered in which the width change ends when the target taper 1 is reached in the anteversion phase, but with this method, it is difficult to complete the width change operation before reaching the target taper 1.
This results in an error in the actual slab width relative to the target slab width. If this error is to be corrected after the width change operation is completed, the short side must be moved in parallel, and when this parallel movement is performed, the shell deformation resistance becomes large (when the width is reduced), and the air gap is This occurs (when expanding the width), making stable continuous casting impossible.

Therefore, the present invention eliminates the error in the target width change amount caused by the difference between the taper amount at the start of the width change and the target taper amount at the end of the width change during the transition from the anteversion period to the rear cheek area. Effective absorption can be achieved by providing the parallel movement period.

Next, a method will be described in which the taper amount is changed during the width change implementation process and an error with respect to the target width change amount that may occur due to the change in the taper amount is absorbed.

In relation to the amount of slab solidification shrinkage, the wider the slab width, the larger the taper amount (smaller the inclination angle β), and conversely, the narrower the slab width, the smaller the taper amount (larger the inclination angle β). known to.

Therefore, when reducing the width of the slab, the chi 74g-
The amount of taper change in the rear cheek area is smaller than the amount of change in
When the width change is completed with the taper amount correctly matching the target value, the width change time will be shortened by T△ shown in Fig. 12,
As a result, the width change amount 1w is short of the target width change amount.

Furthermore, even in the case of expanding the slab width, the amount of taper change during the anteversion period is smaller than the amount of taper change at the rear cheek, and as described above, the width change is completed by correctly matching the taper amount to the target value. Similarly to the width reduction, the width change time is shortened by TΔ, and as a result, the width change amount is short by ΔW.

The shortfall amount ΔW for this target width change amount is the width change □
This is an error with respect to the target width change amount resulting from the difference between the taper amount at the start and the target taper amount at the end of width change. In the present invention, the above-mentioned error is absorbed by performing parallel movement during the transition from the anteversion period to the rear cheek area.

Next, an example of a specific control method for parallel movement that absorbs the error will be explained based on the diagram of FIG. 13. In addition, this Fig. 13 also has the rotation fulcrum at the approximate center position of the short side (t1+12
) is an example.

First, when changing the width, add 1 to the amount of hair at the end of the forward tilt period, and add 1 to the slab width W2 ((1/2
Find the width of the slab.

Once El and W2 are determined, the forward tilting operation is started while maintaining the acceleration rate α$ and the angular velocity ω, which were determined in advance, constant. This forward tilting period is carried out until the taper amount reaches 1, and as soon as it reaches &1, the drive of the swing device is stopped and a transition is made to parallel movement with the horizontal movement speed vh kept constant.

The parallel movement period is continued until the width of the slab reaches W2, and immediately after reaching W2, it moves to the rear cheek part.

The acceleration rate αs in the rear cheek region is only reversed in direction and the absolute value is the same as the acceleration rate in the anteversion phase (1α5
ll=lα521) During the posterior cheek region, the speed increase rate αs and the angular velocity ω are kept constant in the opposite direction to the anteversion phase. Through this ridge tilting operation, the taper amount is sequentially returned to the teniper angle at the start of the width change, but when the taper amount matches the target tenor to 2, the width change ends at that point.

As described above, by setting the taper tE1 at the end of the forward tilting period and the slab width W2 at the end of the parallel movement, taking into consideration the error caused by the shortfall ΔW mentioned above, the error with respect to the target width change amount can be reduced. It can be effectively absorbed by parallel movement during the transition from the anteversion phase to the craniobuccal region.

〔Example〕

The invention was carried out during the production of low carbon At killed steel in a 350 ton/H curved continuous caster. The short side drive device used in this embodiment has the configuration shown in FIG. 5, and both the drive device 13 and the swing device 14 are hydraulic cylinder devices. The equipment specifications and operating conditions of this short side drive device and continuous casting machine are as shown in Table 4.

In this embodiment, the initial speeds rl and r2 are set as shown in Table 1 above with the aim of minimizing the width change time.

On the other hand, since the cylinder capacity of the drive device was insufficient with the value set from the shell strength, the α acceleration rate α$ was determined again from this cylinder capacity.

Therefore, the effective capacity Fav of the cylinder was determined to be (16 tons - 3 tons - 3 tons - 10 tons) 10 tons from the above formula (38). Also, from the profit margin test results of the steel type, Go=2.5X10
((kg/mm2)" @ 8cc), n = 0
．． 32, q=28000 (110K) was obtained. Also, by measuring the shell thickness, Ho = 20 (rrvn/m
1 n 1/2).

Under this condition, the speed increase rate αm is successively changed, and the above (34)
- Required driving force Fi was calculated based on equation (37). As a result, it was found that in order to make the required driving force F less than 10 tons, it was necessary to make the speed increase rate αs less than 50-m1n2. Therefore, the speed increase rate αs was set to 501 mIn2. Along with this, the angular velocity ω is calculated from the above equation (1) as ω=501mun
2/1600m1'1nIn=0.03125 (
rad/min).

The speed increase rate αs1 in the forward tilt period and the speed increase rate αs2 in the rear cheek region are set to αm1=−αs2 in order to improve controllability, as described above.

With the above settings, the horizontal movement speed h and the angular speed ω are determined as follows in the case of width reduction.

Anterior tilt period during width reduction (0≦t≦Tr) V h = 501 + 12.5 (rrul'1
nIn) ω= 0.03125 (rad/rnln
) His cheek area when the width is reduced (Tr≦t≦Tw)V h
= -501+1 00Tr+1 2.5 (
mIvmlo)ω=-0,03125(rad/min
) The turn-back time Tr is determined by the lower F equation (55) from the amount of change S in slab width on one side.

T r-0,2 ((1,5625+8/2) 1/2-
1.25 ) (min) = (55) Now, as mentioned above, set the horizontal movement speed vh and angular velocity ω, move forward to half the width change time Tw, and after reaching half the width Tr, tilt backward. Moved and reduced width. Table 5 shows the width change time relative to the target width change (reduction) amount in comparison with the conventional method. Width reduction by the conventional method was carried out by using two cylinders, upper and lower, as shown in FIG. 3, by increasing the angle of inclination and then moving them in parallel. In this case, in order to suppress the amount of air gap generated to an extent that does not cause large casting defects and to reduce the width by reducing the required driving force to 10 tons or less, the limit for the parallel movement speed Vm was 15rr1rIv/min.

As is clear from Table 5, regardless of the amount of width reduction, the width changing time is significantly shorter in the embodiment of the present invention than in the conventional method. Furthermore, the larger the amount of width reduction, the greater the width change time reduction effect achieved by the embodiment of the present invention.

Next, in the case of width expansion, the horizontal movement speed vh1 angular velocity ω and turning time Tr were determined as follows from Table 3 and equation (56), as in the case of width reduction.

Rear cheek area when width is expanded (O≦t≦Tr) Vh =-50t+12.5 (-mIn)ω=
0.03125 (rad/min) Forward tilt period when width is expanded (Tr≦t≦Tw)Vh-501-100Tr
+ 12.5 (m 1 nin) ω=
0.03125 (red/1nin) T r=0
．． 2 ((1,5625+8/2) 1/2+ 1.2
5) (mln) (56) Table 6 shows the width change time relative to the target width change (reduction) amount in comparison with the conventional method, similar to the width reduction described above.

As is clear from Table 6, even when the width was expanded, the width change time was significantly shortened compared to the conventional method, and no cracks or casting defects were observed.

As described in detail above, by carrying out the present invention, it has become possible to change the width of the mold in a minimum amount of time. Therefore, the portion where the width of the slab changes due to the width change is reduced, and the yield can be significantly improved.

In addition, the slab width can be varied by any amount between 1,300 and 650 plates, and the air gap amount and shell deformation resistance when changing the width can always be kept below the allowable value, resulting in stable slabs without cracking or breakouts. It became possible to operate the

[Brief explanation of drawings]

Fig. 1 (b) is a diagram for explaining the horizontal movement speed of the short side when changing the width according to the present invention, Fig. 2 is a perspective view showing an example of a known variable width mold, Fig. 3 (Ml
, (bj, (C1) and Figures 4 (al, (b), and (c) are schematic diagrams showing an example of a conventional width changing method, where Figure 3 shows width reduction and Figure 4 shows width expansion. Figures 5 to 10 are examples based on the present invention, with Figure 5 being a perspective view showing an example of a short side drive device, and Figure 6 showing the movement of the short side when the width is reduced. FIG. 7 is a schematic diagram showing the movement of the short side when the width is expanded; FIGS. 7(a) and 7(b) are conceptual diagrams explaining the movement of the short side and the conditions for creating the air gap; Figure 8 is for explaining the strain that occurs in slabs when width is changed.
A configuration diagram illustrating the relative movement of the slab and the short side when moving the short side during continuous casting using the short side drive device shown in FIG. acceleration rate α
FIG. 10 is a plan view showing the width changing slab, and FIGS. 11 and 13 are diagrams showing the range of the initial velocity γ on the short side. FIG. 11 and FIG. A diagram for explaining the horizontal movement speed of the short side, and FIG. 12 is a diagram for explaining the error in the width change amount caused by changing the taper amount. 1, la, lb: short side, 2' m, 2 b': long side, ``4; slab, 11; rotating shaft, 12; bearing section, 13; horizontal drive device, 14; turning device, 120: Rotating arm. Agent: Patent attorney Masaaki Akizawa, 2 Mitsugai

Claims (3)

[Claims] (1) In a slab width changing method in which a short side of the mold is moved during continuous casting via a horizontal drive device and a swing drive device that operates independently of the drive device, the short side is moved in the short direction. The side is divided into a forward tilting period in which the sides are sequentially tilted toward the center of the mold, and a backward tilting period in which the sides are sequentially tilted toward the mold center side, and the acceleration rate α_s of the horizontal movement speed of the short side in each period is determined in advance by setting the allowable shell deformation resistance force as a parameter. and the angular velocity ω of the turning device is determined by the following equation (1), and during the period, the width is changed while maintaining the speed increase rate α_s and the angular velocity ω constant. How to change one width. ω=α_s/Uc...(1) However, ω; angular velocity of the turning device (rad/min) α_s;
Acceleration rate of horizontal movement speed of short side (mm/min^2)
Uc: Casting speed (mm/min) (2) Set the maximum permissible horizontal movement speed Vmax of the short side based on the rolling conditions and/or constraints of the short side drive device, and horizontally move the short side during the forward tilting period or backward tilting period in the first half of the width change. When the speed exceeds Vmax, the short side is translated in parallel between the first half and the second half of the width change at a translation speed Vp within the range given by equations (2) and (3) below, thereby eliminating casting defects. 2. A method of changing the width of a slab according to claim 1, wherein the width is changed in the shortest possible time while preventing the occurrence of. ｜Vmax｜≧｜Vp｜・・・・・・(2) Vp≧α_
s1・Tr1... (3) However, Vmax: Maximum allowable horizontal movement speed (mm/min) Vp: Parallel movement speed (
mm/min) α_s1: Acceleration rate of horizontal movement speed of the short side during the forward tilting period or backward tilting period in the first half of width change (mm/min^2) Tr1: Requirement for the forward tilting period or backward tilting period in the first half of width change time (3) Shift the error in the target width change amount caused by the difference between the taper amount at the start of the width change and the target taper amount at the end of the width change from the forward tilt period to the backward tilt period or from the backward tilt period to the forward tilt period. 2. A method of changing the width of a slab according to claim 1, wherein the width of the slab is changed by providing a parallel movement period in between.