JPH0219743B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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. [Prior art] In recent years, in continuous casting, especially continuous casting of steel, it has become necessary to change the slab width without stopping pouring into the mold due to demands for improved operating efficiency and slab yield. Continuous casting methods have come into use. Particularly recently, a method of directly linking the continuous casting process and the rolling process 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 stopping the operation of the continuous casting machine, it is important to make 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 purpose, 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. That is, a pair of short sides 1a and 1b are held between long sides 2a and 2b fixed to a mold vibration table (not shown), and are driven by electric or hydraulic drive devices 3a and 3b attached to the short sides. This device changes the width of the slab 4 without stopping casting. When increasing the width changing speed 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 speeding up of the width changing. As a conventional width changing method, for example, the method disclosed in Japanese Patent Application Laid-Open No. 53-60326 and Japanese Patent Publication No. 54-33772 and shown in FIGS. 3 and 4 is generally practiced. was. That is, FIG. 3 explains the case of width reduction, and the first
In the step, the short side 1 is tilted as shown by the dotted line a, and in the second step it is translated in parallel as shown in b, and then in the third step the slope is returned to the original as shown in c. In this example, in the first step shown by a, the short side 1 is inclined as shown by the dotted line a, in the second step it is translated in parallel as shown in b, and then in the third step the inclination is reduced as shown in c. It shows you how to do it. That is, conventionally, the taper changing operation in FIGS. 3 and 4a and 4c and the parallel movement operation in FIG. 4b were performed completely separately. However, in the conventional method, it takes too much time to change the taper, and even if the parallel movement speed Vm is increased, the effect of reducing the length of the variable width transition part is very small, which hinders the improvement in yield. To solve the above problem, the parallel movement speed Vm
Various attempts have been made to further increase the However, in order to increase the parallel movement speed Vm without breaking the shell solidified in the mold and by overcoming the deformation resistance of this shell,
The tilt change angle Δφ in FIGS. 3 and 4a must be increased. On the other hand, when the inclination change angle △φ is increased, a gap, ie, an air gap, is created between the short side 1 and the slab 4, and when this air gap becomes large, cracks occur in the slab 4, breakout occurs, etc. There is a problem. Therefore, in the conventional method, there is a limit to increasing the parallel movement speed Vm, and there is a limit to shortening the width changing time. In order to solve this problem, the present applicant developed a method in which the upper and lower ends of the short sides are simultaneously moved in the first and third steps to shorten the time required for this period, and the applicant first developed a method to shorten the time required for this period. -184103 and Japanese Patent Application No. 143157/1983. However, even in this method, the basic idea is to perform parallel movement, and although it is possible to make the time to reach parallel movement as fast as possible, it still shortens the total time required for width change. had its limits. [Problems to be Solved by the Invention] The present invention fundamentally solves the problems in the conventional method described above, and further improves the above-mentioned Japanese Patent Application Nos. 57-184103 and 1987-143157. ,
By expanding or reducing the width of the slab during continuous casting in the minimum amount of time, the width change area is reduced and yield is improved, and casting defects such as breakouts (BO) and slab cracks are avoided. The purpose is to provide a method that enables stable operation with no occurrence. [Means for Solving the Problems] The present invention provides a steel continuous casting method in which the short side of the mold is moved during the continuous casting to expand or reduce the slab width. is divided into a forward tilting period in which the mold is sequentially tilted toward the center of the mold and a backward tilting period in which the mold is tilted sequentially toward the mold center. is determined as a parameter, and the difference △V between the moving speeds of the upper and lower ends is determined by the following formula (1), and during the period, the width is changed while maintaining the speed increase rate α and the speed difference △V constant. Concerning the characteristic continuous casting method of steel. △V=α・L/Uc (1) However, △V: Speed difference between the top and bottom ends of the short side (mm/
min) α: Speed increase rate at the top and bottom ends of the short side (mm/min ² ) L: Length of the short side of the mold (mm) Uc: Casting speed (mm/min) In addition, in the above width change, the initial speed at the start of the width reduction change It is preferable to change the width by setting the speed at the lower end of the short side to zero, or to change the width by setting the speed at the upper end of the short side to zero at the time of starting the width expansion change. [Operation] Figure 1 shows the horizontal movement speed (hereinafter referred to as
FIG. 1A shows width reduction and FIG. 1B shows width expansion. The speed was expressed as + (positive) for the speed of movement toward the center of the mold, and - (negative) for the speed of movement toward the side away from the center of the mold. First, the case of width reduction will be explained based on FIG. 1a. In the figure, the broken line x indicates the moving speed (hereinafter referred to as the top end speed, expressed as Vu) of the top end of the short side (the position corresponding to the meniscus in the mold, and hereinafter referred to as the top end of the short piece). ,
The solid line y is the moving speed of the lower end of the short side (the lower end of the short side refers to the lower end of the short side, expressed as Vl). When reducing 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 it reaches approximately half of the target width change, it is moved in parallel. Immediately perform a backward tilting operation to tilt the short side toward the side opposite to the center of the mold, and the series of width changing operations is completed. The example in Figure 1 shows two types of width change patterns, where the target width change amount is represented by width change times Tw ₁ and Tw ₂ , and the turnaround time from the forward tilt period to the backward tilt period is Tr ₁ and Tr. Expressed as ₂ . FIG. 5 is a schematic diagram showing the movement status of the short side during width reduction, and during the forward tilting period, the upper end speed Vu of the short side is changed to the lower end speed.
By always moving at a constant speed faster than Vl, the inclination angle β of the short side 1 with respect to the horizontal line z indicated by the dashed-dotted line gradually increases, and the amount of forward inclination increases. Conversely, during the retrograde phase, the lower end velocity Vl is lower than the upper end velocity Vu.
By always increasing the speed at a constant speed, the inclination angle β
gradually becomes smaller, and the amount of forward tilt decreases. (In the present invention, the period of movement in which the inclination angle β increases, that is, toward the center of the mold, is the forward tilt period, and conversely, the period of movement in which the inclination angle β becomes smaller, that is, the period of movement in which the inclination angle β becomes smaller, that is, toward the center of the mold.) (The period was defined as a backward tilting period and used.) On the other hand, the upper and lower speeds Vu and Vl have a constant speed increase rate α in the forward tilting period, that is, in the forward tilting period, the positive direction, that is, the forward tilting amount increases sequentially. In the backward tilt period, the speed increase α is used in the negative direction, that is, the speed increase rate α in which the backward tilt amount increases sequentially (if the positive direction is used as a reference, it is the deceleration rate, but in the present invention, it is unified to the speed increase rate, and it is When it is necessary to specifically express the speed increase rate α, the speed increase is expressed as (+) and the deceleration is expressed as (-). However, the amount of forward tilt or backward tilt increases with time. In Fig. 1, the speed increase rate in the forward lean phase is expressed as a1, the speed difference between the upper and lower end speeds Vu and Vl is expressed as △V ₁ , and the speed increase rate in the backward lean phase of deceleration is expressed as α ₂ ,
α ₂₁ , and the speed difference between the upper and lower end speeds Vu and Vl is △V ₂ ,
Expressed as △V ₂₁ . Next, the case of width expansion will be explained based on the schematic diagrams of FIG. 1b and FIG. 6. When widening the width, contrary to the width reduction described above, the short side is moved in the direction away from the center of the mold, but in the first half, the lower end speed Vl is always kept at a constant speed than the upper end speed Vu. Immediately after performing a backward tilting operation to increase the movement by a predetermined amount, a forward tilting operation is performed to increase the upper end speed Vu from the lower end speed Vl. In this case as well, the upper and lower end velocities Vu and Vl have a constant acceleration rate α as described above, and the amount of forward inclination or the amount of backward inclination increases with time. As described above, in the present invention, the speed increase rate α is determined and set in advance according to the steel type, slab size, casting speed, etc. using the allowable shell deformation resistance as a parameter, as will be described later. Determine the speed difference △V of the speed Vl based on the above formula (1),
By maintaining the width constant and changing the width during each of the anteversion period and the retroversion period, we succeeded in achieving various great effects as described below. The driving device for the short side is limited to the driving device shown in FIG. 2 as long as it can control the speeds Vu and Vl of the upper and lower ends of the short side to predetermined speeds as described above. isn't it. For example, there is a well-known device as shown in FIG. 19, in which a device 1 is provided on the back surface of the short side 1 and is movable in the horizontal direction and swingable by the rotational drive of a cam mechanism 14 with a spherical seat 12 as a fulcrum. It is also possible to use a structure in which a book spindle 13 is connected and the spindle 13 moves the short side 1 in the horizontal direction and rotates at the same time. In FIG. 19, reference numeral 15 denotes an electric motor, which moves the spindle 13 in the horizontal direction via a screw shaft 16. However, in the experience of the present inventors, the first
In the apparatus shown in Fig. 9, for example, as the width change speed is increased, the short side 1 is moved away from the spherical seat 12, that is, as the width of the slab is narrowed, the upper or lower end of the short side 1 is moved in the casting direction. There has been a shift, especially recently.
In curved molds that are being actively adopted, the above-mentioned deviation creates a gap between the long side and the short side,
It may induce casting defects. Taking these points into consideration, a mold with a structure driven by two cylinder devices, upper and lower in the casting direction as shown in FIG. . Next, the reason why the width change of the present invention can be efficiently implemented by using the speed increase rate α and speed difference ΔV 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 to prevent BO and defects in the slab from occurring during the width change. To achieve this, during the entire period of width change implementation, it is necessary to always ensure proper pushing in so that no air gap is created between the slab and the short side, and the slab is not pushed in excessively by the short side. It is essential to do so. FIG. 7 is a conceptual diagram illustrating the movement of the short side and the conditions for generating the air gap, where Xu and Xl are arbitrary points at the upper and lower ends of the short side (any time t from the start of width change).
β indicates the inclination angle between the aforementioned short side and the horizontal line z at the relevant time point,
Further, θ represents the inclination angle with respect to the vertical line as θ=β−90°. Now, suppose that the upper end of the short side moves by dXu and the lower end moves by dXl during a minute time dt. During this time, the slab moves downward by [Uc・dt], where the casting speed is Uc,
Point d in Figure 7a moves to point _d1 , and point e moves to point _e1 . If the distance traveled by short side 1 during this time is small,
This results in the formation of the air gap (η in FIG. 7a) between the short side and the slab. In order to avoid this, the short side should move by more than [Uc·dt·tanθ] during dt, as shown in FIG. 7b. In other words, regarding the amount of movement of the upper end of the short side and the amount of movement of the lower end, the following (2),
It is sufficient if equation (3) holds true. dXu≧Uc・dt・tanθ −(2) dXl≧Uc・dt・tanθ −(3) Here, since tanθ can be expressed by the following equation (4), it can be divided by dt in the above equations (2) and (3). , the following equations (5) and (6) can be obtained. tanθ=(Xu−Xl)/L −(4) dXu/dt=Vu≧(Xu−Xl)・Uc/L−(5′) Vu−(Xu−Xl)・Uc/L≧0 −(5) dXl/dt=Vl≧(Xu−Xl)・Uc/L (6′) Vl−(Xu−Xl)・Uc/L≧0 −(6) Therefore, the upper end speed Vu and the lower end speed Vl are
It has been found that if the equations (5) and (6) are set so as to always be satisfied, the width can be changed without causing the air gap η. Next, the total amount of deformation (hereinafter referred to as the indentation amount δ) that any point on the slab undergoes while passing through the mold will be explained based on FIG. Point d generated at the upper end of the short side at arbitrary time t passes through the lower end of the short side after L/Uc time. If the short side is moving at this time, the slab is deformed by the difference from the lower end position of the short side at the time T=t+L/Uc and leaves the mold. The total amount of deformation that the slab receives when passing through the mold, that is, the amount of indentation δ can be expressed by the following equation (7). δ=Xl(t+l/Uc)−Xu(t)−(7) Therefore, the indentation state of the slab is expressed by the indentation amount δ and the conditions that do not cause the air gap mentioned above.
It has been found that by controlling these two conditions so as not to change with respect to the elapsed time during the width change, it is possible to maintain a stable pressed state in which the above-mentioned casting defects do not occur. Therefore, the present inventors further continued their research in order to satisfy the above conditions. Now, in order to satisfy the above conditions, (5) to
It is necessary to find Vu and Vl that simultaneously satisfy equation (7). The following equations (8), (9) and (10) are equivalent to the above equations (5), (6) and (7).
)
These are the expressions obtained by differentiating each expression with respect to time,
By combining these (8) to (10), the following equation (11) is obtained. dVu/dt-Uc/L・(Xu-Xl)=0 −(8) dVl/dt−Uc/L・(Vu−Vl)=0 −(9) Vl(t+l/Uc)−Vu(t)= 0 −(10) dVu/dt={Vu(t) −Vu(t−L/Uc)}/(L/Uc) −(11) The solution to the above equation (11) can be expressed as a general solution equation as follows. This becomes equation (12). Vu=A·t+B −(12) In equation (12), A and B are constants. Further, by substituting the above equation (12) into the above equation (9), Vl can be expressed by the following equation (13). Vl=A・t+(B−A・L/Uc) −(13) In other words, from equations (12) and (13), in order to maintain the stable pushing state described above, Vu and Vl must be adjusted from the start of width change. A new finding was obtained that it is sufficient to set it as a linear function with the elapsed time t, and that it is sufficient to always maintain a constant speed difference between Vu and Vl. Based on this knowledge, the present inventors conducted further research on changing the width during continuous casting in actual operations, and as a result, the constant A in equations (12) and (13) above was determined using the allowable deformation resistance as a parameter. It was confirmed that it is possible to apply the above findings on an industrial scale by setting the following conditions. In the present invention, the constant A has a value other than zero, and therefore Vu and Vl are accelerated or decelerated with time. During this width change period, Vu and
In the present invention, the constant A that accelerates or decelerates Vl is used as the speed increase rate α. The constant B in equations (12) and (13) is the initial speed at the start of changing the width of the upper end of the short side, and may be appropriately determined in advance depending on the width changing and the operating conditions at that time. When the speed increase rate α is set, the speed difference between Vu and Vl can be calculated from the short side length L of equation (13) and the casting speed Uc as follows: △V=Vu−Vl=α・L/Uc −(1) , and the above-mentioned equation (1) is obtained. Incidentally, if the speed increase rate α is zero, △V in the above equation (1) = 0.
Therefore, Vu=Vl, that is, the speeds of the upper and lower ends of the short side are the same speed. This results in the same state as the parallel movement in width change in the conventional method. It is true that during the parallel movement period of the conventional method, the indentation state is kept stable, so no casting defects occur in this part.
Conventionally, a width change pattern has been implemented centering on this parallel movement. However, as mentioned above, in this conventional method, an inclination angle changing period is required before and after the parallel movement period, and it is difficult to secure an appropriate pushing amount during this period, and there is a limit to shortening the width changing time. There were some problems that occurred. The present invention makes it possible to fundamentally solve the conventional problem by setting the speed increase rate α to a value other than zero and determined from the allowable shell deformation resistance force. Next, a specific method for determining the speed increase rate α will be explained. Now, as the speed increase rate α increases, the width change time will be shortened, but if it exceeds a certain value, the slab will buckle and the shell on the surface will break, or the deformation resistance will increase and the width change time will be shortened. This causes phenomena such as the inability to change the width due to insufficient driving force to move the sides. As a result of repeating many experiments, the present inventors confirmed that it is possible to determine the optimum range of the speed increase rate α from the allowable shell deformation resistance force. The allowable shell deformation resistance force may be determined from the shell strength or from the short side driving force of the mold. First, we will explain how to determine it from the strength of the slab shell. When a slab is pushed into the mold by the short sides of the mold, a solidified shell, that is, a shell, formed on the surface of the slab is strained. At this time, a resistance force corresponding to the strain rate is generated in the shell. However, if the resistance force exceeds the critical strength of the shell, buckling deformation of the shell occurs, resulting in casting defects.
In order to avoid the occurrence of such defects, the strain rate occurring in the shell must be lower than the critical strain rate corresponding to the shell strength. The strain rate of the shell in the width changing method of the present invention will be explained based on FIG. 9. Let dX(E) be the minute amount of indentation at a position at an arbitrary distance E from the top end of the short side, and if the top end moves dXu and the bottom end moves dXl during a minute time dt, the slab at the point E is affected. The minute indentation amount dX(E) can be expressed by the following equation (14). dX(E)={(dXl−dXu)/L}・E +dXu−Uc・dt・tanθ−(14) Therefore, the pushing rate per unit time can be expressed by the following equation (15). dX(E)/dt=(Vl−Vu)・E/L +Vu−Uc・tanθ−(15) By the way, the first half of the width change (when the width is reduced is the anteversion phase,
In the backward tilting phase when the width is expanded), Vu and Vl can be expressed by the following equations (16) and (17) as described above. Vu=α ₁・t+B ₁ −(16) Vl=α ₁・t+B ₁ −α ₁・L/Uc −(17) However, α ₁ ; Acceleration rate in the first half of the width change B ₁ ; In the first half of the width change Initial velocity of the upper end of the short side Also, the latter half of the width change (backward tilting period when the width is reduced, and forward tilting period when the width is expanding) can be expressed by the following equations (18) and (19). Vu=α ₂・(t-Tr)+B ₂ −(18) Vl=α ₂・(t-Tr)+B ₂ −α ₂・L/Uc
−(19) However, α ₂ ; Acceleration rate B ² in the second half of the width change; Initial speed Tr of the upper end of the short side in the second half of the width change; Turning time from the first half to the second half Therefore, the above (16), Substituting equation (17) into equation (15) above and considering tanθ=(Xu-Xl)/L, the push-in rate for the first half is given by equation (20) below. dX(E)/dt=B ₁ − α ₁・E/Uc − (20) Similarly, the push-in rate in the second half is expressed by the following formula (20'). dX(E)/dt=B ₂ −α ₂・E/Uc−α ₁・Tr
−(20′) If we divide {dX(E)/dt) in the above formulas (20) and (20′) by half (1/2)・W of the slab width 2W handled by one short side, the width can be changed. Strain rate of slab in the first half and second half ε〓 ₁ (E)
and ε〓 ₂ (E) are obtained as shown in equations (21) and (22) below. ε〓 ₁ (E)=(B ₁ −α ₁・E/Uc)・1/W −(21) ε〓 ₂ (E)=(B ₂ −α ₂・E/Uc−α ₁・Tr)・1/W
-(22) This can be illustrated as shown in FIGS. 10 and 11. That is, FIG. 10 shows width reduction;
Figure a shows the first half, and Figure 10 b shows the second half. or,
Figure 11 shows the width expansion; Figure 11a is the first half;
Figure 11b shows the second half. Figures 10 and 11
In the figure, the vertical axis is the vertical distance from the meniscus, the horizontal axis is the strain rate ε〓, and the strain rate ε〓 at the upper and lower ends, respectively.
α and B are determined by setting . By the way, if the strain rate ε becomes negative (-), an air gap will occur, and if it exceeds a certain value, the slab will buckle, making stable casting impossible as described above. Therefore, the appropriate range of strain rate ε〓 is greater than or equal to zero and less than or equal to the allowable maximum value ε〓max (0
≦ε〓≦ε〓max). As a result of various investigations regarding the above ε〓max, the present inventors found that ε〓max differs between the upper and lower parts of the slab, and that by applying the values shown in Table 1 for steel types manufactured by ordinary continuous casting, It was confirmed that the functions of the present invention could be reliably exhibited.

[Table] Therefore, from equations (21) and (22) above, the upper end of the first half is the following equation (23), and the lower end is the following equation (24).
Similarly, the following equation (25) holds true for the upper end in the second half, and the following equation (26) holds true for the lower end. 0<B ₁ /W≦ε〓max ₁ −(23) 0<(B ₁ −α ₁・L/Uc)・1/W≦ε〓max ₂ −(24) 0<(B ₂ −α ₂・Tr)・1/W≦ε〓max ₁ −(25) 0<(B ₂ −α ₂・L/Uc−α ₁・Tr)・1/W≦
ε〓max ₂ − (26) The correlation for satisfying each of the above formulas, that is, maintaining stable casting during width changes, is summarized as follows.
Each equation (a) to (h) is found. B ₁ ＞0 −(a) B ₁ ＞α ₁・L／Uc −(b) B ₁ ＜W・ε〓max ₁ −(c) B ₁ ＜W・ε〓max ₂ ＋α ₁・L／Uc − (d) B ₂ ≧α ₁・Tr −(e) B ₂ ≧α ₁・Tr+α ₂・L/Uc −(f) B ₂ ≦W・ε〓max ₁ +α ₁・Tr −(g) B ₂ ≦ W・ε〓max ₂ +α ₁・Tr+α ₂・L/Uc −(h) Figure 12 shows the relationship between (a) to (h) in the first half and second half, as described above. Figure 12a
shows the first half, and Figure 12b shows the second half. Furthermore, the horizontal axis shows the speed increase rates α ₁ and α ₂ , and the vertical axis shows the initial speed B ₁ ,
_B2 . The hatched portion D in FIG. 12 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 acceleration rates α ₁ and α ₂ to arbitrary values within the range of the hatched portion D, the above-mentioned width change of the present invention can be implemented. Moreover, the above α ₁ ,
B ₁ and B ₂ are also determined by setting α ₂ . By the way, as mentioned above, width changes are required to be carried out as quickly as possible.
It is necessary to find the speed increase rate α within the range of the hatching portion D that satisfies this requirement. Therefore, in the first half of the width reduction, the acceleration rate α ₁ and the initial speed B ₁
are both positive, and the larger their absolute values, the better. From this, point A shown in FIG. 12a becomes the optimum condition. That is, it is sufficient if B ₁ =α ₁ ·L/Uc=W ·ε〓max ₁ −(27). In the second half of the period, the inclination angle that was made during normal operation in the first half of the period must be returned to its original value, so α ₁・Tr=−α ₂・(Tw−Tr) −(28) Tw−Tr=−(α ₁ /α ₂ )·Tr −(29) Therefore, in order to reduce the width change time, the larger the absolute value of α ₂ is, the more important it becomes, and the point C shown in FIG. 12B becomes the optimum point. That is, it is sufficient if B ₂ =α ₁ ·Tr = W ·ε〓max ₂ + α ₁ ·Tr + α ₂ ·L/Uc − (30). Next, in order to shorten the width change time in the first half of width expansion, the smaller both α ₁ and B ₁ , the better. Therefore, point A shown in FIG. 12a becomes the optimum condition, and the initial speed _B1 is as follows. B ₁ = 0 = W・ε〓max ₂ + α ₁・L/Uc − (31) Also, in the latter half of width expansion, the relational expression Tw−Tr=−(α ₁ /α ₂ )・Tr − (32) Since α ₁ <0 and α ₂ >0 in the equation, the larger α ₂ is, the better in order to reduce the width change time.
Therefore, point E shown in Figure 12b becomes the optimal point,
The initial velocity _B2 is as follows. B ₂ = α ₁・Tr + α ₂・L/Uc = W・ε〓max ₁ + α ₁・Tr − (33) As shown above, the speed increase rate α that minimizes the width change time
and the initial velocity B, which are listed in Table 2 below.

[Table] Therefore, the upper and lower end speeds under the conditions shown in Table 2 above
Vu and Vl are as shown in Table 3 (width reduction) and Table 4 (width expansion) below.

【table】

〔Example〕

Low-coal Al in a 350 ton/H curved continuous casting machine
The invention was implemented during the production of killed steel. The equipment specifications and operating conditions of this continuous casting machine are as shown in Table 5.

[Q: Target width variable (reduction) amount/mm one side]

Now, as mentioned above, the upper and lower speeds Vu and Vl were set, and during the width variable time, the width was moved forward to half the amount Tr of Tw, and after reaching the half amount Tr, the width was reduced by moving backward. FIG. 16 shows a comparison of the width change time with respect to the target width change (reduction) amount with the conventional method, where the solid line is the embodiment of the present invention and the broken line is the conventional method. In FIG. 16, the horizontal axis shows the width reduction amount Qmm/one side, and the vertical axis shows the width change time Tw. Further, the width reduction by the conventional method was carried out by the method shown in FIG. In this case, the limit for the parallel movement speed Vm was 35 mm/min 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 7 tons or less. According to Figure 16, regardless of the size of the width reduction amount,
It can be seen that the width changing time is shorter in the embodiment of the present invention than in the conventional method. Further, as the amount of width reduction increases, the effect of shortening the width change time according to the embodiment of the present invention increases. FIGS. 17a and 17b show changes in the shell deformation resistance force acting on the upper and lower cylinders with time from the start of width change in width reduction in the conventional method (a) and the embodiment (b) of the present invention. In the figure, the solid line indicates the required driving force acting on the upper cylinder, and the broken line indicates the required driving force acting on the lower cylinder. The maximum required driving forces Fu max and Fl max of the upper and lower cylinders shown in FIGS. 17a and 17b are approximately the same for both the conventional method and the example, and the required driving force did not increase by implementing the present invention. Furthermore, in the case of the conventional method, the air gap generated was a maximum of 1.5 mm, but in the case of the present invention, it was almost zero, and no internal or surface defects were observed. Next, in the case of width expansion, the vertical velocity Vu of the short side 1,
Vl is set, and the velocity pattern of the upper and lower cylinders is determined by the following equations (63) to (66). Retroversion phase during width expansion (0≦t≦Tr) Vu=−50t (mm/min) −(63) Vl=20−50t(mm/min) −(64) Forward tilt phase during width expansion (Tr ≦t≦Tw) Vu=20−50(Tw−t)(mm/min) −(65) Vl=−50(Tw−t)(mm/min) −(66) Also, width change time Tw and turning The time Tr is given by the following equations (67) and (68). Tr=0.2{(1+0.5Q) ^1/2 +1}(min) −(67) Tw=0.4{(1+0.5Q) ^1/2 +1}(min) −(68) [Q: Width expansion amount mm/ One Side] FIG. 18 shows the width change time based on this embodiment in comparison with the conventional method. In FIG. 18, the horizontal axis shows the width expansion amount Qmm/one side, and the vertical axis shows the width change time Tw. Further, the solid line in the figure shows the embodiment of the present invention, and the broken line shows the conventional method. Width expansion using the conventional method is carried out using the method shown in Figure 4, and the parallel movement speed |Vm| is adjusted to keep the air gap amount below the allowable value and the required driving force within 7 tons, as in the case of width reduction. The limit was 15 mm/min. In this width expansion, as in the case of width reduction, it can be seen that the width changing time is significantly shorter in the embodiment of the present invention than in the conventional method, regardless of the amount of width expansion. Also, regarding the amount of air gap generated and the required driving force, the amount of air gap generated is almost zero,
The required driving force for the lower cylinder was 7 tons or less, and as in the case of width reduction, each was within the allowable values. (Effects of the Invention) As detailed above, by carrying out the present invention, the width of the mold can be changed in a minimum amount of time. Therefore, the area where the width of the slab changes due to width changes can be reduced.
Yield can be significantly improved. In addition, the slab width can be varied by any amount between 1300 and 650 mm, and the air gap amount and shell deformation resistance can always be kept below the allowable value when width is changed, resulting in stable operation without slab cracking or breakouts. becomes possible.

[Brief explanation of drawings]

Figures 1a and b are diagrams for explaining the horizontal movement speed of the upper and lower ends of the short sides when changing the width according to the present invention, and Figure 2 is a perspective view showing an example of a known variable width mold. Fig. 3 a, b, c and 4
Figures a, b, and c are schematic diagrams showing an example of a conventional width changing method, in which Fig. 3 shows a case of width reduction, and Fig. 4 shows a case of width expansion. Figures 5 to 18 show examples based on the present invention, where Figure 5 is a schematic diagram showing the movement of the short side when the width is reduced, and Figure 6 is a schematic diagram showing the movement of the short side when the width is expanded. Schematic diagrams, Figures 7a and 7b are conceptual diagrams explaining the movement of the short sides and the conditions for generating air gaps, and Figure 8 is a conceptual diagram explaining the total amount of deformation that any point on the slab undergoes while passing through the mold. Conceptual diagram. Figure 9 is a conceptual diagram explaining the strain rate of the shell in the width changing method of the present invention. Figures 10 a, b and 11 a, b show the relationship between the strain rate of the shell and the acceleration rate. 10 shows a case where the width is reduced, and FIG. 11 shows a case where the width is enlarged. Figures 12a and b are diagrams showing the ranges of α and B where casting defects do not occur, Figure 13 is a structural diagram showing the arrangement of the upper and lower cylinders that drive the short sides, and Figure 14 is the width reduction. Fig. 15 is a diagram showing another example of the moving speed of the upper and lower ends of the short side when
Figure 6 is a diagram showing the width change time relative to the target width change (reduction) amount in comparison with the conventional method example, Figure 17 a, b
18 is a diagram showing changes over time from the start of width change in the shell deformation resistance force acting on the upper and lower cylinders during width reduction in the conventional method and the embodiment of the present invention. FIG. FIG. 3 is a diagram showing a comparison of time with a conventional method. FIG. 19 is a cross-sectional structural diagram showing another example of the short side drive device. 1, 1a, 1b; short side of the mold; 2a, 2b; long side of the mold; 3a, 3b; drive device; 4: slab.

Claims (1)

[Claims] 1. In a continuous casting method for steel in which the short side of the mold is moved during continuous casting to expand or reduce the width of the slab, the short side is moved before the short side is sequentially tilted toward the center of the mold. The acceleration rate α of the horizontal movement speed of the upper and lower ends of the short side in each period is determined in advance using the allowable shell deformation resistance force as a parameter. A continuous casting method for steel, characterized in that the difference △V in the moving speed of the parts is determined by the following formula (1), and the width is changed while maintaining the speed increase rate α and the speed difference △V constant during the period. . △V=α・L/Uc (1) However, △V: Speed difference between the top and bottom ends of the short side (mm/
min) α: Speed increase rate at the top and bottom ends of the short side (mm/min ² ) L: Length of the short side of the mold (mm) Uc: Casting speed (mm/min) 2 Initial speed at the bottom end of the short side at the start of width reduction change The method according to claim 1, wherein the width is changed as zero. 3. The method according to claim 1, wherein the width is changed by setting the initial speed at the upper end of the short side to zero at the time of starting the width expansion change.