JPH0557066B2 - - 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 reason, it has become necessary to increase the width change speed. To change the slab width in continuous casting, an operation is performed in which the short mold piece 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 in the horizontal direction by a drive device (not shown), so that the slab 4 This is a device that changes the width of the mold 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,
As shown in Publication No. 49173, this is carried out by a single spindle connected to the back of the short piece, which is movable in the horizontal direction and is configured to be swingable by the rotational drive of a cam mechanism using a spherical seat as a fulcrum. I was worried.
That is, the spindle can move in the horizontal direction and rotate at the same time, but when actually changing the width, the short side is tilted to a predetermined angle by a cam mechanism and then maintained in that state. Generally, the width is changed at a very slow speed. On the other hand, as disclosed in, for example, Japanese Patent Application Laid-Open No. 53-60326 and Japanese Patent Publication No. 54-33772,
Attempts are being actively made to install two electric or hydraulic drive devices in the vertical direction of the short side and control these two drive devices, respectively, to change the width at high speed. . 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. In the first step indicated by a, the short side 1 is inclined as shown by the dotted line a, and in the second step b
After parallel movement as shown, then in the third step c
4 shows a method of returning the inclination to its original value, and FIG.
After parallel movement as shown in b in the second step, the third step
Step c shows how to reduce the slope. 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. However, in order to increase the parallel movement speed Vm without breaking the shell solidified in the mold and to overcome the deformation resistance of this shell, the angle of inclination change △φ must be increased. I have a problem to say. 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 change time. In order to solve this problem, the applicant moves the upper and lower ends of the short sides simultaneously in the first step and the third step,
A method for shortening the time required for this period was developed and filed as Japanese Patent Application Laid-Open Nos. 59-73155 and 60-33855. 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 is still necessary to shorten the total time required to change the width. has reached its limit. [Problems to be Solved by the Invention] The present invention fundamentally solves the problems in the conventional methods described above, and further improves the above-mentioned JP-A-59-73155 and JP-A-60-33855. ,
In molds equipped with a horizontal drive and a swivel drive that operates independently of the drive, width changes during continuous casting that expand or reduce the width of the slab can be made in a minimum amount of time. The purpose of this invention is to provide a method that improves yield by reducing BO and enables stable operation without the occurrence of casting defects such as breakouts (hereinafter referred to as BO) and cracking of slabs. [Means for Solving the Problems] The configuration of the present invention for solving the above problems will be described below. First, an example of a short-side drive device applied to the present invention will be explained based on FIG. 5. In FIG. 5, 1 indicates the short side of the mold, and a bearing 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 (hereinafter referred to as a drive device) 13 is connected to the rotation shaft 11 . A rotating arm 120 is protruded from the bearing portion 12 , and a rotating arm 120 includes a rotating drive device that is placed on the horizontal drive device 13 and operates independently of the horizontal drive device 13 . (hereinafter referred to as a turning device) 14 are connected. Therefore, by driving the drive device 13 back and forth, the short side 1 is moved in the horizontal direction. In addition, by driving the turning device 14, the short side 1 becomes the turning axis 1.
Rotates around 1 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. In general, the position of the center of gravity is determined by the ratio (l1/l
2) is in the range of 2-5. Of course, the swivel device 1
4, or depending on the arrangement of equipment near the short side, etc., the position of the rotating shaft 11 may be approximately at the center of the short side 1, or at any position in the casting direction. It is also possible to set it to . The rotation operation can be performed independently of the movement of the short side 1 in the horizontal direction (hereinafter referred to as horizontal movement). In other words, the rotation operation can be performed while horizontally moving the short side, and the rotation operation can also be performed even when the horizontal movement is stopped. In the present invention, when the horizontal drive device 13 and the swing drive device 14 are collectively referred to as a 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 short side 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 sequentially tilted toward the mold center side, and the acceleration rate of the horizontal movement speed of the short side in each period is calculated. α _s is determined in advance using the allowable shell deformation resistance force as a parameter, and the angular velocity ω of the turning device is determined by the following formula (1), and during the period, the speed increase rate α _s and the angular velocity ω are kept constant and the width is It is characterized by making changes. ω＝α _s /U _c ...(1) However, ω: Angular velocity of the swing device (rad/min) α _s : Acceleration rate of horizontal movement speed of the short side (mm/min)
min ² ) U _c ; Casting speed (mm/min) In addition, in the width changing method described above, rolling conditions and
Alternatively, the maximum allowable horizontal movement speed Vmax of the short side is set based on the constraints of the short side drive device, and when the horizontal movement speed of the short side during the forward tilting period or backward tilting period of the first half of width change exceeds the above Vmax. In order to prevent the occurrence of casting defects, the short side is translated in parallel between the first half and the second half of the width at a translation speed Vp within the range given by equations (2) and (3) below. It becomes possible to change the width in time. ｜Vmax｜≧｜Vp｜ …(2) Vp≧α _s 1・T _r 1 …(3) However, Vmax: Maximum allowable horizontal movement speed (mm/min) Vp: Parallel movement speed (mm/min) α _s 1; Increase 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 ) T _r 1; Required time for the forward tilting period or backward tilting period in the first half of width change Furthermore, in the width changing method, the error with respect to 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 from the forward tilt period to the backward tilt period or from the backward tilt period to the forward tilt period. It is preferable to absorb by providing a parallel movement period during the transition to the phase. [Function] 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. 1st
Figure a shows the width reduction, and Figure 1 b shows the width expansion.The horizontal movement speed is defined as positive (plus) for the movement towards the center of the mold and negative (minus) for the movement towards the side away from the center of the mold. expressed. In addition, the rotation speed is expressed by the angular velocity ω of the rotation device, and the inclination angle β shown in FIG.
The direction in which the angle of inclination β increases, that is, the direction in which the short side leans toward the center of the mold, is positive (plus), and conversely, the direction in which the inclination angle β decreases, that is, the direction in which the short side leans away from the center of the mold, is negative ( (minus). First, the case of width reduction will be explained based on FIG. 1a. In the figure, the solid line a represents the horizontal movement speed Vh of the short side,
The solid line b is the angular velocity ω of the swing device. 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. Without doing so, 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. FIG. 6 is a schematic diagram showing the movement of the short side when the width is reduced. Horizontal movement speed of the short side during the width change operation
Vh is a constant acceleration rate α _s during the longitudinal tilt period (the period in which the forward tilting operation is performed is called the forward tilting period, the period in which the backward tilting operation is performed is called the backward tilting period, and these are collectively referred to as the longitudinal tilting period). , that is, the speed increase rate α _s at which the moving speed increases in the forward direction, that is, toward the center of the mold, in the forward tilting phase, and
In the backward tilting phase, the speed increasing rate α _s decreases the moving speed toward the negative direction, that is, toward the mold center. If it is necessary to express them separately, increase in speed will be expressed as (+) and deceleration will be expressed as (-). In addition, when referring to this collectively, it will be hereinafter referred to as the speed increase rate α _s . ], each of which increases or decreases over time. As described later, the speed increase rate α _s is determined in advance using the allowable shell deformation resistance force as a parameter. On the other hand, the short side in the forward tilting phase is rotated while being controlled to a constant angular velocity ω in the positive direction determined by the above _equation (1) based on the casting speed during the operation and the speed increase rate α s. The inclination angle β of the short side 1 with respect to the horizontal line z indicated by the dashed line in the figure gradually increases, and the amount of forward inclination gradually increases. On the other hand, during the backward tilt period, the short side rotates at a constant angular velocity ω in the negative direction, and the inclination angle β gradually decreases, so that the amount of forward tilt decreases. In Fig. 1, the speed increase rate in the forward tilt period is represented by α _s 1 and the angular velocity is represented by ω1, and the speed increase rate in the backward tilt period is represented by α _s 2 and the angular velocity is represented by ω2. The turnaround time is shown as Tr, and the total time required to change the width is shown as Tw. Next, the case of width expansion will be explained based on the schematic diagrams of FIG. 1b and FIG. 7. When enlarging 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 short side is rotated at a constant angular velocity ω in the negative direction. As described above, the rearward tilting and movement is performed at a horizontal movement speed having a constant speed increase rate α _s , and after the predetermined amount of movement is performed, the angular velocity is immediately switched to the positive direction and the forward tilting operation is performed. Even in this forward/backward tilting operation for widening the width, the horizontal movement speed of the short side has an acceleration rate α _s and is accelerated or decelerated with time. In addition, in Fig. 1 above, the first half of the width change (when the width is reduced is the retroversion phase,
The reason for the deviation in the horizontal movement speed Vh when transitioning from the forward tilt period (when the width is expanded) to the latter half (the backward tilt phase when the width is reduced, and the forward tilt phase when the width is expanded) is due to the rotation of the short side. This is due to the fact that the pivot point deviates from its center position (l1>l2) as shown in FIG.
l2), the above-mentioned deviation does not occur, and the horizontal movement speed Vh at the end of the first half becomes the horizontal movement speed Vh at the beginning of the rearward tilting period or the forward tilting period of the second half. As described above, in the present invention, the speed increase rate α _s 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. (1)
By determining the width based on the formula and changing the width while keeping it constant during each of the anteversion period and the retroversion period, we succeeded in achieving various great effects as described below. Next, the reason why the width change of the present invention can be efficiently implemented by using the speed increase rate α _s and the 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 to prevent defects from occurring in the BO or slab during the width change. To achieve this, it is necessary to ensure proper pushing at all times 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 piece during the entire width change implementation period. That is essential. FIG. 8 shows using the short side drive device of FIG. 5,
It is a block diagram explaining the relative movement of a slab and a short side when moving a short side during continuous casting. Based on FIG. 8, we will first explain the strain that occurs in the slab when the width is changed. In FIG. 8, 1u is a part corresponding to the meniscus of the short side, 1l is the lower end of the short side, β is the inclination angle between the short side and the horizontal line z, and
The angle of inclination with respect to the vertical line is expressed as θ (θ=β−90°). Assume that the short side 1 is at a position B1 at a certain time t, and moves to a position B2 during a minute time dt. The horizontal movement speed during this minute time dt is Vh, and the angular velocity is ω. Also, minute time dt
During this period, the short side meniscus equivalent portion 1u moves by dYu, and the short side lower end 1l moves by dYl. At this time, the slab 4u that was in the meniscus equivalent part 1u at time t is
After time dt, the slab 4l located at the lower end 1l of the short side moves to 4l1. This travel distance is [Uc・
dt]. As the short side moves from B1 to B2, the slab is apparently pushed in by dYu at the part corresponding to the meniscus and dYl at the lower end of the short side, but in reality, as mentioned above, the slab is pushed into [Uc・dt] , from moving downward,
Horizontal displacement due to this movement [Uc・dt・tanθ]
The deformation of the minute is alleviated. Therefore, if the amount of deformation actually experienced by the slab is ηu at the meniscus-equivalent part and ηl at the lower end of the short side, then 7μ and ηl are 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 the inclination angle of the short side is between dt. If dθ is displaced to
dYu and dYl can be expressed by the following formulas (6) and (7). dYu=l1・tan(θ+dθ)+dX−l1・tanθ……(6) dYl=−l2・tan(θ+d)+dX−(−l2・tanθ)
...(7) However, l1: Distance from the meniscus equivalent part 1u to the drive device (rotation shaft 11 in Fig. 5) l2: From the lower end of the short side 1l to the drive device (rotation shaft 11 in Fig. 5) Since the distance θ is small, the following approximate formula holds true. tanθ≒θ ……(8) Substituting the above equation (8) into the above (6) and (7) gives the following (9) and (10)
The following equations (11) and (12) are obtained by substituting equations (8) to (10) into equations (4) and (5). dYu＝l1・dθ＋dX …(9) dYl＝−l2・dθ＋dX …(10) dηu＝l1・dθ＋dX−Uc・dt・θ …(11) dηl＝−l2・dθ＋dX−Uc・dt・θ … …(12) Dividing equations (11) and (12) by dt gives the following (13) and (14)
Find the formula. dηu/dt=ηu=l1・dθ/dt+dX/dt−Uc・θ
...(13) dηl/dt=η・l=l2・dθ/dt+dX/dt−Uc・θ
...(14) Here, dηu/dt=η·u, dηl/dt=η·l represent the actual amount of deformation per unit time, that is, the deformation speed.
Further, dθ/dt represents the time change in the inclination angle of the short side, that is, the angular velocity ω. Further, 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, by dividing the above equations (13) and (14) by half W of the slab width 2W, the strain rate ε· can be obtained from the following equations (15) and (16). ε・u=l1・ω/W+Vh/W−Uc・θ/W
...(15) ε・l=−l2・ω/W+Vh/W−Uc・θ/W
...(16) In order not to change the strain rate over time, that is, to keep the deformation of the slab always appropriate, [dε・u/dt
=0] and [dε·l/dt=0]. Therefore, it is sufficient if the conditions of equations (17) and (18) below are satisfied. dε・u/dt=(l1/W)・dω/dt+(1/W)・
dVh/dt−(Uc/W)・ω≡0 …(17) dε・l/dt=(−l2/W)・dω/dt+(1/
W)・dVh/dt−(Uc/W)・ω≡0 ...(18) From equations (17) and (18), the following equation (19) can be found. dω/dt=0...(19) Solving equation (19) yields equation (20) below, and substituting equation (19) into equations (17) and (18) above yields equation (21) below. . ω=β ...(20) However, β: integral constant dVh/dt=Uc・ω ...(21) Since the right side of the above equation (21) is a constant with respect to time, if we set it as A, we get (22 ) is expressed as the formula. dVh/dt=Uc・ω≡A...(22) By solving equation (22), the general solution can be found as shown in (23) below. Vh=A・t+γ...(23) However, γ: Integral constant Also, the following (1)' can be found from the above equation (22). ω=A/Uc ……(1)′ In other words, from equations (23) and (1)′, in order to keep the deformation of the cast side at an appropriate level without changing the strain rate over time as described above, it is necessary to New knowledge that it is sufficient to set the horizontal movement velocity Vh as a linear function of the elapsed time t from the start of the width change, and that the angular velocity ω is always kept at a constant value determined from A and the flank velocity Uc. was gotten. 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 (23) and (1)' was determined to be a value using the allowable deformation resistance as a parameter. It was confirmed that it is possible to apply the above knowledge on an industrial scale by setting . The constant A in the present invention has a value other than zero, and therefore the horizontal movement speed Vh is increased or decreased with time. During this width change period
In the present invention, the constant A that accelerates or decelerates Vh is used as the speed increase rate α _s . Also, (23) and (1)'
The integral constant γ in the equation is the initial speed of the horizontal movement speed Vh at the start of 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 α _s is set, the angular velocity ω is determined from the casting speed Uc during the operation as follows: ω=α _s /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 the width change, it was found that it is sufficient to keep the acceleration rate α _s of the horizontal movement speed Vh and the angular velocity ω constant, and the The angular velocity ω is the speed increase rate α _s and the slab velocity
It can be obtained from Uc using the above equation (1). Therefore, if α _s is positive, ω will also be positive, and the short side will tilt forward. Conversely, if α _s 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.
In order to perform a series of width changes, at least one or more periods are required for each positive and negative period of α _s . Various width changes are possible by combining the positive and negative periods of α _s ,
Among these, the simplest one and the highest speed can be obtained when α _s is configured with one positive and one negative α s as shown in FIG. In other words, this is a case where the entire width change period is divided into a forward tilt period and a backward tilt period. Therefore, the horizontal movement speed of the first half and the second half of the width change
Vh and angular velocity ω are subscripts (1 is the first half,
2 can be expressed as follows by adding the latter half). First half Vh1=α _s 1・t+γ1 ……(24) ω1=α _s 1/Uc ……(25) Second half Vh2=α _s 2・t+γ2 ……(26) ω2=α _s 2/Uc ……( 27) By substituting equations (24) to (27) into equations (15) and (16) above, the strain rate for each period can be found as shown in equations (28) to (31) below. First half ε・u1=(l1/W)・(α _s 1/Uc)+γ1/W
...(28) ε・l1=(−l2/W)・(α _s 1/Uc)+γ1/W
...(29) Second half ε・u2=(l1/W)・(α _s 2/Uc)+γ2/W−α _s
1・Tr/W……(30) ε・l2=(−l2/W)・(α _s 2/Uc)+γ2/W−α
_s
1.Tr/W...(31) By the way, if the strain rate ε is negative, an air gap will occur, and if it exceeds a certain value, the driving force of the short side drive device will increase significantly, or the slab will sit. This causes a bending phenomenon and makes stable casting impossible. Therefore, the strain rate ε· in equations (28) to (31) above must satisfy the following conditions. 0≦ε・ij≦ε・maxi ...(32) However, i: the meniscus equivalent part u of the short side, or the lower end lj: the first half or the second half of the width change Therefore, the above (28) to (31) When formula (32) is substituted into formula, the following (33) to (36) hold true. 0≦(l1/W)・(α _s 1/Uc)+γ1/W≦ε・max
u...(33) 0≦(-l2/W)・(α _s 1/Uc)+γ1/W≦ε・
max l...(34) 0≦(l1/W)・(α _s 2/Uc)+γ2/W−α _s 1・
Tr/W≦ε・max u……(35) 0≦(−l2/W)・(α _s 2/Uc)+γ2/W−α _s
1・Tr/W≦ε・max l ...(36) The correlations for satisfying each of the above formulas, that is, maintaining stable casting during width changes, are summarized as follows.
Each equation (a) to (h) is found. γ1≧−l1・(α _s 1/Uc) ……(a) γ1≧W{ε・max u−(l1・W)・(α _s 1/Uc)}
=
−l1/(α _s 1/Uc) + W・ε・max u …(b) γ1≧l2・(α _s 1/Uc) …(c) γ1≧l2・(α _s 1/Uc)+W・ε・max l ……(d) γ2＞α _s 1・Tr−l1・(α _s 2/Uc) ……(e) γ2≦−l1・(α _s 2/Uc)+α _s 1・Tr+W・ε・
max u...(f) γ2＞α _s 1・Tr+l2・(α _s 2/Uc) ……(g) γ2≦l2・(α _s 2/Uc)+α _s 1・Tr+W・ε・max
l...(h) Figure 9 shows the relationship between (a) to (h) by dividing it into the first half and the second half. Figure 9 a is the first half, and Figure 9 b is indicates the second half. Furthermore, the horizontal axis represents the speed increase rates α _s 1 and α _s 2, and the vertical axis represents the initial speeds γ1 and γ2. The hatched portion D 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 α _s 1, α _s 2 and the initial speeds γ1, γ2 to arbitrary values within the range of the hatched portion D, the above-mentioned width change of the present invention can be implemented. 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 _s within the range of the hatching portion D that satisfies this requirement. In the first half of the width reduction, the speed increase rate α _s is positive, and the larger its absolute value, the better. From this, the point P1 shown in FIG. 9a becomes the optimum condition. Also, in the first half of the width expansion, the speed increase rate α _s is negative, and the larger its absolute value is, the more the speed increase rate α s is negative. Therefore, point P3 is optimal. Next, in the second half of the width change, the inclination angle that was made during normal operation in the first half must be returned to its original value, so ω1・Tr=−ω2・(Tw−Tr) ……(37) ω1=α Since _s 1/Uc, ω2=α _s 2/Uc, Tw−Tr=−(α _s 1/α _s 2)・Tr ……(38), and in order to reduce the width change time, α _s 2 The larger the absolute value of is, the better. In the case of width reduction, the optimum point is the point P2 shown in FIG. 9b, and in the case of width expansion, the point P4 shown in FIG. 9a is the optimum point. As described above, the speed increase rate α _s for minimizing the width change time is determined, and Table 1 below shows it as a list.

[Table] The horizontal movement speed Vh and angular velocity ω under the conditions shown in Table 1 are as shown in Table 2 (width reduction) and Table 3 (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 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. Now, in this embodiment, the initial speeds γ1 and γ2 are set as shown in Table 1 above with the aim of minimizing the width change time. On the other hand, the α acceleration rate α _s was determined from the cylinder capacity since the cylinder capacity of the drive device was insufficient with the value set from the shell strength.

【table】

[Table] Therefore, the effective capacity Fav of the cylinder is (38) above.
From the formula (16 ton - 3 ton - 3 ton = 10 ton) it became 10 ton. Also, from the tensile test results of the steel type, Go=2.5×
10 ^-12 {(Kg/mm ² ) ⁿ・Sec}, n=0.32, q=28000
(1/°K) was determined. Further, the shell thickness was measured and found to be Ho=20 (mm/min ^1/2 ). Under this condition, the speed increase rate α _s is successively changed, and the above (34) to (37)
The required driving force F was determined based on the formula. As a result,
It has been found that in order to reduce the required driving force F to 10 tons or less, the speed increase rate α _s needs to be 50 mm/min ² or less. Therefore, the speed increase rate α _s was set to 50 mm/min ² .
Along with this, the angular velocity ω is calculated from equation (1) above: ω=50mm/
min ² /1600mm/min=0.03125 (rad/min). The speed increase rate α _s 1 in the forward tilt period and the speed increase rate α _s 2 in the backward tilt period are set to α _s 1 = α _s 2 in order to improve controllability, as described above. With the above settings, the horizontal movement velocity Vh and angular velocity ω are determined as follows in the case of width reduction. Forward tilt period when width is reduced (0≦t≦Tr) Vh=50t+12.5 (mm/min) ω=0.03125 (rad/min) Backward tilt period when width is reduced (Tr≦t≦Tw) Vh=−50t+100Tr+12 .5 (mm/min) ω=-0.03125 (rad/min) The turn-back time Tr is determined by the following formula (55) from the change amount S of slab width on one side. Tr=0.2 {(1.5625+S/2) ^1/2 −1.25} (min)
...(55) Now, as mentioned above, we set the horizontal movement speed Vh and angular velocity ω, moved forward to half the amount Tr of the width change time Tw, and after reaching the half amount Tr, moved backward to reduce the 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 a level that does not cause large casting defects, and to reduce the width with the required driving force of 10 tons or less, the parallel movement speed Vm is 15.
mm/min was the limit.

[Table] As is clear from Table 5, 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 reduction.
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 Vh, angular velocity ω, and turning time Tr were determined as follows from Table 3 and Equation (56), as in the case of width reduction. Backward tilting period when width increases (0≦t≦Tr) Vh=-50t+12.5 (mm/min) ω=-0.03125 (rad/min) Forward tilting phase when width increases (Tr≦t≦Tw) Vh= 50t−100Tr+12.5 (mm/min) ω=0.03125 (rad/min) Tr=0.2{(1.5625+S/2) ^1/2 +1.25}(min)−
(56) Table 6 shows a comparison of the width change time with respect to the target width change (reduction) amount with the conventional method, similar to the width reduction described above. As is clear from Table 6, the width changing time could be significantly shortened compared to the conventional method even when width was expanded, and no casting defects were observed at all.

[Table] (Effects of the Invention) As detailed above, by carrying out the present invention, it has become possible to change the width of the mold in a minimum amount of time. For this reason, the portion where the width of the slab changes due to the width change can be reduced, and the 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 force can always be kept below the allowable value when changing the width, resulting in stable operation without slab cracking or breakouts. became possible.

[Brief explanation of drawings]

FIGS. 1a and 1b are diagrams 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, and FIGS. b, c and FIGS. 4a, b, c are schematic diagrams showing an example of a conventional width changing method, with FIG. 3 showing width reduction and FIG. 4 showing width expansion. 5 to 10 show examples based on the present invention, FIG. 5 is a perspective view showing an example of a short side drive device, FIG. 6 is a schematic diagram showing the movement status 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, Fig. 7 a and b are conceptual diagrams explaining the movement of the short side and the conditions for generating the air gap, and Fig. 8 is a schematic diagram showing the movement of the short side when the width is changed. This diagram is for explaining the strain that occurs in the slab, and is a configuration diagram illustrating the relative movement between 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. , FIG. 9 is a diagram showing the speed increase rate α _s and the range of the short side initial velocity γ without causing casting defects, FIG. 10 is a plan view showing the width-changed slab, and FIG.
13 and 13 are diagrams for explaining the horizontal movement speed of the short side when changing the width according to another embodiment of the present invention, and FIG. 12 shows the error in the width change amount caused by changing the taper amount. FIG. 1, 1a, 1b...short side, 2a, 2b...long side, 4...cast side, 11...rotating shaft, 12...bearing section, 13...horizontal drive device, 14...swivel device,
120... Rotating arm.

Claims (1)

[Claims] 1. A slab width changing method in which the 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, comprising:
The movement of the short side is divided into a forward tilt period in which the short side is sequentially tilted toward the center of the mold, and a backward tilt period in which the short side is 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. 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 according to (1) below, and during the period, the width is changed while maintaining the speed increase rate α _s and the angular velocity ω constant. A method for changing slab width during continuous casting, characterized by: ω＝α _s /U _c ...(1) However, ω: Angular velocity of the swing device (rad/min) α _s : Acceleration rate of horizontal movement speed of the short side (mm/min)
min ² ) U _c ; Casting speed (mm/min) 2 During continuous casting, the width of the slab is changed by moving the short side of the mold via a horizontal drive and a swing drive that operates independently of the drive. In the method,
The movement of the short side is divided into a forward tilt period in which the short side is sequentially tilted toward the center of the mold, and a backward tilt period in which the short side is 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. is determined in advance using the allowable shell deformation resistance force as a parameter, and the angular velocity ω of the rotating device is determined in advance.
is determined in (1) below, and during the period, the speed increase rate α _s and the angular velocity ω are kept constant, and further, the maximum allowable horizontal movement speed of the short side is determined based on the rolling conditions and/or the constraints of the short side drive device.
Vmax is set, and the horizontal movement speed of the short side in the forward tilting phase or backward tilting phase of the first half of the width change is
When exceeding Vmax, the short side is translated at a translation speed Vp within the range given by equations (2) and (3) below between the first half and the second half of the width change to prevent the occurrence of casting defects. A method for changing the width of a slab during continuous casting, characterized by changing the width in the shortest possible time while preventing ω＝α _s /U _c ...(1) However, ω: Angular velocity of the swing device (rad/min) α _s : Acceleration rate of horizontal movement speed of the short side (mm/min)
min ² ) U _c casting speed (mm/min) |Vmax|≧|Vp| …(2) Vp≧α _s 1・T _r 1 …(3) However, Vmax; Maximum allowable horizontal movement speed (mm/min) min) Vp: Parallel movement speed (mm/min) α _s 1: Increase 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 ) T _r 1: Width change The time required for the first half of the forward tilting phase or backward tilting phase.