JPH0446665B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for supporting the short side of a slab in continuous casting equipment. BACKGROUND ART Conventionally, in a continuous casting machine, as shown in FIG. A support device 3 is provided. When changing the width of the slab during pouring in such a continuous casting machine, for example, when narrowing the width of the slab as shown in FIG. After the tapered part 7 has completely passed through, the slab support device 3 is placed in a position to support the slab after the dimensions have been changed.
The support plate 5 is moved. As described above, the conventional slab support device 3 does not support the tapered part 7 of the slab 6 that occurs when changing the width of the slab, so the slab pulling speed is significantly slower than the normal pulling speed. By increasing the amount of cooling water sprayed onto the surface of the slab per unit time, the growth of a shell (solidified shell) that forms from the surface of the slab inward is promoted. Forms a shell that is thicker than when it is filled, causing deformation (bulging, etc.) due to the static pressure of the unsolidified molten steel inside.
They had taken apparent measures to prevent this. Therefore, a decrease in productivity and a deterioration in slab quality due to fluctuations and decreases in casting speed were unavoidable. Furthermore, a device of the type shown in FIG. 2 has been proposed as a support device for the short side of a slab. This uses a guide roller 8 in place of the support plate 5 shown in FIG. As shown in FIG. 2, in a slab short side support device of the type that constantly presses the supporting member against the short side of the slab 6 using a cylinder 9 or the like, it is difficult to set the pressing force. That is, if the pressing force of the support member is too strong,
Stress that exceeds the allowable range will be generated in the shell, which will cause defects such as cracks in the internal solidification area.On the other hand, if it is too weak, the short side of the slab will be caused by the bulging phenomenon and the slab will protrude. The supporting member is pushed back in the opposite direction, and as a result, it becomes impossible to support the slab, resulting in a breakout. Further, in the tapered portion, since the shell thickness is not constant, even if the pressing force of the support member is constant, a pushing action may be applied to the shell. Problems to be Solved by the Invention In the lower part of the mold of a continuous slab casting machine, the solidified shell of the slab is thin, and the long sides have noticeable bulging due to static iron pressure. It is also essential that the slab be supported at all times by a slab support device. However, regarding the short side,
Since the amount of bulging is extremely small compared to the long side, the importance of the slab support device is low, and instead of supporting the slab in close contact all the time like on the long side, it is possible to maintain a small distance between the slab and the slab. It has been found that it is sufficient to install a slab support device and support the slab only when the slab is about to bulge beyond the allowable bulging amount. Therefore, the first object of the present invention is to effectively support the tapered part of the slab that occurs when changing the width of the slab, so that the tapered part of the slab can be effectively supported without slowing down the slab drawing speed when changing the width of the slab. It is possible to change the width of the slab while suppressing the bulging phenomenon of the tapered part to below the allowable value.
An object of the present invention is to provide a method for supporting the short side of a slab in continuous casting equipment. A second object of the present invention is to avoid applying a pushing action to the shell of the slab more than prevents it from expanding due to the bulging phenomenon when changing the width of the slab;
To realize the above-described method for supporting the short side of a slab by effectively supporting the slab without causing excessive strain and without being pushed back by the slab that overhangs due to the bulging phenomenon. That's true. Means for Solving the Problems Therefore, in order to improve the above-mentioned conventional drawbacks, according to the present invention, a plurality of position-controlled short side supports of the cast slab are provided at the rear stage of the short side movable wall constituting the mold. The device is arranged along the drawing direction of the slab, parallel to the plane in the thickness direction passing through the center line of the slab, and facing the short side surface of the slab, and when changing the width of the slab,
The width of the cast strip at the position corresponding to each of the short side support devices of the tapered portion of the short side surface of the cast strip that occurs in the width direction of the slab due to the movement of the short side movable wall of the mold is determined by the short side movable wall. is calculated based on the amount of movement of the slab width, and the minimum distance between the inclined virtual slab short side surface of the tapered part and each of the slab short side support devices corresponding to the calculated slab width is constant. Then, each of the slab short side support devices is independently displaced in the width direction of the slab, and when the short side surface of the slab short side extends in the width direction due to bulging, only the overhanging portion is moved into the casting slab. Provided is a method for supporting a short side of a slab in continuous casting equipment, characterized in that the short side of a slab is supported by a short side support device. As described above, in the method for supporting the short side of a slab in continuous casting equipment according to the present invention, a plurality of position-controlled short side supporting devices of the slab are used as the short side supporting devices of the slab. Furthermore, when changing the width of the slab, the virtual short side of the slab at the tapered part is predicted and the amount of bulging on the short side of the slab is allowed. Each slab short side support device is arranged so that when the slab reaches the short side support and comes into contact with the short side support when the slab reaches the desired value and is about to bulge further, the bulging part is supported by the short side support. The supports are independently displaced in the width direction of the slab following the movement of the movable wall on the short side of the mold. With this configuration, when changing the width of the slab, each slab short side support device approximately follows the width of the slab that is generated by changing the width of the slab, so that bulging is prevented at the tapered part of the slab that occurs when changing the width of the slab. Even if bulging occurs, if the amount of bulging exceeds the allowable value, the bulging part of the slab will be supported when it comes into contact with the support on the short side of the slab, and the progress of overhang of the slab due to bulging will be prevented. can. Therefore, it is possible to prevent bulging from proceeding beyond the allowable value range, and there is no need to slow down the slab drawing speed when changing the width of the slab. Furthermore, since a plurality of position-controlled slab short side support devices are used as the short side support device for the slab, the pressing force of the short side support member of the short side of the slab can be reduced. It is not too strong to generate excessive stress on the shell, and conversely, it is too weak to prevent the supporting member on the short side of the slab from being pushed back in the opposite direction by the slab protruding due to the bulging phenomenon. Embodiments Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 3 shows an apparatus for carrying out the method of the invention. In the figure, reference number 1 indicates a mold, which is configured to have a rectangular cross section by a long side fixed wall (not shown) and a short side movable wall 2, and the short side movable wall 2 is connected to a mold width variable device 11. Therefore, it can move in the width direction of the slab 6 (see arrow A). As can be seen from the drawing, on the lower side in the lengthwise direction of the slab 2 of the short side movable wall 2 constituting one side of the mold 1, that is, at the rear stage, there is a wall that passes through the center line of the slab 6 along the drawing direction F of the slab 6, as can be seen from the drawing. The slab support 14 of the first slab short side support device 12 and the second slab short side support device 13 parallel to the thickness direction surface and with respect to the short side surface of the slab.
The slab supports 17 are arranged so as to face each other. In the illustrated embodiment, the first slab short side support device 12 supports its short side support body on the support plate 1.
4, and the slab 6 is supported by the support plate 14, and the support plate 14 is connected to the spindle 15.
It can be moved in the width direction of the slab 6 by the worm screw screw 16 (see arrow B). The second slab short side support device 13 is of a type in which the slab short side support is a support roller 17, and the slab 6 is supported by the roller 17. Similarly, it can be moved in the width direction of the slab 6 by means of the spindle 15 and the worm screw screw 16 (see arrow C). Note that the short side support devices 12 and 13 for the slab short side are exemplified in such a manner that the short side support is a combination of an upper support plate 14 and a lower support roller 17; The lower part may be a support plate, or a support plate and a support plate, or a support roller and a support roller. Figure 4 shows the slab tapered part 18 and the first and second slab short side support devices 1 when narrowing the width of the slab.
2 and 13. Note that the solid line 6A showing the contour of the slab shows the slab without any bulging, and the dotted line 6B indicates the slab is supported on the short side supports 14 and 17 with bulging. It shows the state in which In the present invention, in a state where the slab does not bulge at all, the short side supports 1 of the first and second short side supports 12 and 13 of the slab
4 and 17 are controlled in position to be close to the short side surface of the slab tapered portion 18 but not in contact with it. Therefore, as can be understood from FIG. 4, when the short side movable wall 2 of the mold 1 is moved inward to narrow the width of the slab 6, the slab 6 will move in the direction in which the slab 6 is pulled out. Since it tapers towards the end and widens towards the end,
The lower ends of the short side supports 14 and 17 of the first and second short side support devices 12 and 13 and the short distance between the short side supports 14 and 17 of the short side of the slab (when the slab does not bulge at all). The distance from the side surface is the narrowest and the minimum distance. Conversely, if the short side movable wall 2 of the mold 1 is moved outward to widen the width of the slab 6, the slab 6 becomes tapered in the direction in which the slab 6 is pulled out. Since it is tapered, the short side support body 14 of the short side support device 12, 13
The distance between the upper end of the cast slab 17 and the short side surface of the slab tapered portion 18 (in a state where the slab does not bulge at all) is the narrowest and minimum interval. In FIG. 4, the minimum spacing is indicated by reference numeral 19. If the amount of bulging exceeds the allowable value, the slab will have internal cracks. If the amount of bulging becomes even larger, breakout will occur. Therefore, the above-mentioned minimum interval is set to such an extent that the amount of bulging is suppressed to the extent that defective slabs do not occur. If the minimum distance is set in this way, even if bulging occurs, the minimum distance between the imaginary short side surface of the slab tapered portion 18 (in a state where no bulging has occurred in the slab) will be set. The short-side supports 14 and 17, whose positions are controlled so as to maintain the slab at a constant value, hold the slab in such a way that the bulging that tends to exceed the tolerance is stopped at the tolerance without pushing the slab. support. Here, the amount of bulging of a slab is influenced by many factors such as slab width, casting speed, casting temperature, cooling rate, solidification thickness, depth from the molten metal surface, roll pitch, and roll diameter. Currently, it is difficult to specify the bulging limit at which defects occur in slabs using theoretical calculation formulas. However, if we dare to provide a reference value regardless of the low accuracy, an example would be as follows. The following example is based on Tetsu to Hagane Vol. 67 (1981) No. 8, page 1173.
As shown in FIG. 6, this model is based on a model in which a slab moves on horizontally arranged entry and exit rolls. δ=βt _c ⁿ /h ³ sin (π・x/a) …(1) β=12(1−ν ² )・d・a ₀・q・a ⁴ …(2) However, δ: Bulging amount β: Coefficient for determining δ t _c : Creep time h: Shell thickness x: Distance from entry roll a: Roll pitch ν: Poisson's ratio d: Shape factor a ₀ : Creep constant q: Molten steel static pressure n: Constant (depends on temperature and steel type) From this bulging amount δ, bulging strain ε _b is calculated by the following formula. ε _b =1600・δ・h/a ² (%) ...(3) However, ε _b : Bulging strain δ : Bulging amount h : Shell thickness a : Roll pitch The limit of bulging strain ε _b varies depending on the steel type, but
If additional strain increases due to misalignment, roll reduction, etc. are ignored, it is generally considered that ε _b ≦0.2 to 0.3 (%). If ε _b = 1600・δ・h/a ² ≦0.3, then δ≦0.3×a ² /1600h The shell thickness h at the part 1 to 1.5 m directly below the mold is when the slab drawing speed V≒2.0 m/min , 20
~25 mm, and roll pitch a = 200 ~ 250 mm. δ=0.3×200 ² /1600×20=0.375 δ=0.3×250 ² /1600×25=0.46875 Therefore, δ=0.4 to 0.5 mm is obtained, which corresponds to the fixed minimum interval set in the present invention. do. In actual operation, δ = 0.3 to 5 due to differences in operating conditions, slab support mechanisms, and uncertain high-temperature physical properties of steel.
mm would be considered as the minimum spacing. Next, a case will be described in which the method for supporting the short side of a slab according to the present invention is carried out using the above-mentioned apparatus. (1) First, when changing the width of a slab during casting, move the short side movable wall 2 of the mold 1 to a desired width position. (2) Next, the cast strip is removed at a position corresponding to each of the short side supports of the tapered portion 18 of the short side surface of the cast strip, which is generated in the width direction of the slab due to the movement of the short side movable wall 2 of the mold 1. Calculate the width based on the amount of movement of the short side movable wall 2. Here, with reference to FIG. An example of a calculation formula for calculating the single width W ₂ based on the amount of movement of the short side movable wall will be explained. In FIG. 5, each symbol indicates the following. Z: Moving speed of short side movable wall (mm/min) V: Slab drawing speed (mm/min) L ₁ : Distance from the bottom end of the mold to the bottom end of the short side support 14 of the slab (mm) W ₁ : Width of narrowed slab at mold exit (mm) W ₂ : L ₁ mm below the mold (point A)
Slab width at (mm) W ₀ : Slab width before width change (mm), that is, interval between movable walls on the short side of the mold before width change t: Elapsed time after width change (min) First, t=0 When the narrow width is started at , the slab width (W ₂ ) at the mold exit, that is, at the point L ₁ mm below the bottom end (point A), is calculated as follows. When t=0, the slab leaving the mold is L ₁ /
Point A is reached after V minutes. Therefore, the slab width W ₂ at point A at time t=L ₁ /V is W ₀ , while the width W ₁ of the slab at the mold exit is:
It is expressed as below. W ₁ =W ₀ −2Z·t (4) In the above equation (4), Z, that is, the moving speed of the movable wall on the short side of the mold, is set and input by the control device. Therefore, the width W ₁ of the slab at the mold exit is determined by changing the width W 1 from the initial value W ₀ at the time of width change to the moving speed Z of the short side movable wall and the elapsed time t.
The moment-to-moment value can be found by subtracting the double value of the product of . The slab width W ₂ at point A after t (t≧L ₁ /V) minutes is expressed as follows. Therefore, W ₂ = W ₁ {1−(T ₀ −T ₁ )×1.2×10 ⁻⁵ } = {W ₀ −2・Z・(t−L ₁ /V)}×{1−(T ₀ −T ₁ )×1.2×10 ^-5 } ...(5) However, T ₀ is the solidus temperature of molten steel, which varies depending on the steel type. For example, low carbon steel has approx.
1520℃, and about 1440 for structural steel (S50C)
It is ℃. T ₁ is the slab surface temperature at point A, and is measured, for example, with a radiation thermometer. The temperature for low carbon steel is approximately 1300℃. An example of actually applying the above slab width calculation formula (5) when the width is narrow is shown below.

【table】

[Table] As described above, the slab width W ₂ at the lower end of the slab short side support 14 can be calculated based on the amount of movement of the short side movable wall. It goes without saying that the slab width W ₃ at the lower end of the slab short side support 17 can be determined in the same way as the slab width W ₂ at the lower end of the slab short side support 14. , I understand. Therefore, in the following explanation,
The short side supporter 14 of the cast strip will be explained, and the description of the short side supporter 17 of the cast strip will be omitted. From this slab width W ₂ , the virtual (ideal) slab width is determined by the movement of the short side movable wall 2, and the position of the sloping ``virtual slab short side surface'' of the tapered part corresponding to the slab width is determined. is required. As is clear from the above equation (5), this virtual slab short side surface is calculated from the slab width W ₀ before width change, the moving speed Z of the short side movable wall, the slab withdrawal speed V, etc. This is the theoretical value. Therefore, in the above equation (5), W ₀ ,
By substituting the values of Z, L ₁ , V, T ₀ and T ₁ , t=
The slab width W ₂ at point A is calculated from 0 to every Δt=(=0.5 to 5 seconds), and the position of the virtual short side surface of the slab after t minutes is calculated. In this way, each slab short side support 1 at the time of width change
The position of the slab tapered portion 18 corresponding to Nos. 4 and 17 is determined at intervals of several seconds (0.5 to 5 seconds) while the slab taper portion 18 passes. On the other hand, the slab short side support devices 12 and 13 are equipped with synchro transmitters 21 and 22 that detect the rotation angle of a motor that rotates in response to a movement command from a control device, and signals from the synchro transmitters 21 and 22 are provided. Accordingly, the position of each slab short side support device 12, 13 can be known. (3) Therefore, when the position of the short side of the slab is calculated as described above, the position of each of the short side supports 14 and 17 of the slab with respect to the short side can be calculated, so that the inclination of the tapered portion 18 can be calculated. The width of the short side movable wall is adjusted so that the narrowest distance between the short side of the virtual slab and each of the short side support devices 12 and 13, that is, the minimum interval 19, is always a constant interval. Following the replacement displacement operation, each of the slab short side supports 14 and 17 is independently displaced. The independent displacement of the cast strip short side supports 14 and 17 is carried out by independently operating the respective drive motors M of the respective cast strip short side supports 14 and 17. Here, the minimum interval is controlled to be kept constant as follows. To explain with reference to Fig. 5, when width change (narrow width) is started from time 0, the lower end of the mold (exit)
The slab width at is narrowed at a speed of Z. After the width narrowing starting point passes point A (the position of the lower end of the support body 14), the support device 12 starts moving after δ/Z time (the support device 13 starts moving in the same way). V (pulling speed) = 1.5 m/min, Z (short side moving speed) = 25 mm/min, δ (allowable bulging amount) = 3 mm
Then, δ/Z = 7.2 (seconds), that is, 7.2 seconds after the narrowing start point passes point A (passing distance 180 mm)
The slab short side support device 12 starts moving.
Point A (position L ₁ mm below the mold outlet, that is, the position of the lower end of the short side support 14 of the short side support device 12) and point B (position L ₂ mm below the mold exit, In other words, the position of the short side support body 17 of the short side support device 13)
The width of the slab is determined by equation (5), the amount of bulging is determined by equations (1) and (2), and the short side supporting devices 12 and 13 of the slab are positioned at positions based on the results. An arithmetic processing device (not shown) is provided for the above-mentioned arithmetic processing. The processing unit has
The variables of equation (5), equation (1), and equation (2) described above are input. These variables can be set automatically or manually when changing the width. A control device (not shown) is further provided to control the positioning of the short side supporting devices 12 and 13 based on the calculation results. 0.5~ for the arithmetic processing device and position control device
Tracking is performed at 5-second intervals, the data is processed, and commands are issued to the supporting devices 12 and 13 on the short side of the slab. The short side support devices 12 and 13 of the slab received the command.
operates the motor M to drive each worm jack screw 16, and the short side supports 14 and 17 of the slab are moved or displaced in the width direction of the slab. On the other hand, the movement or displacement of the short side supports 14, 17 is constantly detected by synchro transmitters 21, 22.
7 is once stopped when it is displaced by an amount equal to the movement amount instructed by the position control device, and remains stopped until it starts operating with the next command. Therefore, it is moved intermittently at tracking intervals of 0.5 to 5 seconds. That is, as shown in FIG. 4, when the slab 6 tapers toward the drawing direction of the slab, each short side support body 14 is arranged parallel to the center line of the slab 6. . The positions of the side supports 14 and 17 are controlled. After the width of the slab passing through point A (point B) reaches _W1 , the supporting devices 12 and 13 are positioned according to the width of the slab. (4) When the short side of the short side of the slab in the tapered part overhangs in the width direction due to bulging beyond the minimum interval 19, only the overhanging part is positioned at a distance of the minimum interval 19. It is supported by the short side support body, and is appropriately supported without pressing the overhanging portion more than necessary and without insufficient supporting force. In addition, in the above control, it is not detected at all whether or not the short side surface of the slab protrudes in the width direction due to bulging. When the short side surface of the tapered part on the short side of the slab overhangs in the width direction beyond the minimum distance 19 due to bulging, only the overhanging portion is supported by the short side support of the slab. Effects of the Invention As explained above, in the short side supporting method of the present invention, a plurality of position control type short side supporting devices of the slab are used as the short side supporting devices of the slab, and the short side of the slab is The sides can be supported at multiple points, and furthermore, when changing the width of the slab, it is possible to predict the virtual short side of the slab in the tapered part that will occur when changing the width of the slab. Each slab short side support member is independently displaced in the width direction of the slab so as to substantially follow the width of the slab. With this configuration, only when the short side surface of the tapered part of the slab overhangs in the width direction due to the bulging and comes into contact with the short side support of the slab, only this overhanging part supports the short side of the slab. supported by the body. In addition, since the short side support device for the slab is of a position control type, there is no need to press the short side of the slab more than necessary, there is no lack of supporting force, and the support of the short side is appropriate. Therefore, high-quality slabs can be manufactured with high productivity.

[Brief explanation of the drawing]

1 and 2 are views showing a short side support device for a cast strip according to the prior art, and FIG. 3 is a view showing a short side support device for a cast strip for carrying out the method of the present invention. , Figure 4 is a diagram showing the positional relationship between the slab tapered part and the first and second slab short side support devices when narrowing the slab width, and Figure 5 is a diagram showing the positional relationship between the slab taper part and the first and second slab short side support devices when narrowing the slab width. FIG. 6 is a schematic diagram illustrating the state in which the width of the slab changes when the slab width changes. FIG. 6 is a schematic diagram of a model for analyzing bulging. [Main reference numbers], 1: mold, 2: short side movable wall, 6: slab, 12: first slab short side support device, 13: second slab short side support device, 14: support Plate, 15: spindle, 17: support roller.

Claims (1)

[Claims] 1. A plurality of position-controlled slab short side support devices are installed behind the movable short side wall that constitutes the mold along the direction in which the slab is pulled out, parallel to the plane in the thickness direction that passes through the center line of the slab. and is arranged so as to face the short side surface of the slab, and when changing the width of the slab, the taper portion of the short side surface of the slab that occurs in the width direction of the slab due to the movement of the short side movable wall of the mold. The slab width at the position corresponding to each slab short side support device is calculated based on the amount of movement of the short side movable wall, and the inclined virtual slab width of the tapered part corresponding to the calculated slab width is calculated. Each of the short side supporting devices of the slab is independently displaced in the width direction of the slab so that the minimum distance between the side surface and each of the short side supporting devices of the slab is kept constant. A method for supporting the short side of a cast strip in continuous casting equipment, characterized in that when the short side of the side protrudes in the width direction due to bulging, only the protruding portion is supported by the short side supporting device of the cast slab. .