JP2018012117A - Manufacturing method of thin-wall cast piece and manufacturing device of thin-wall cast piece - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a thin-wall cast piece capable of shortening a casting length of a non-steady part, suppressing fracture of the cast piece and stably manufacturing thin-wall cast piece.SOLUTION: A manufacturing method of a thin-wall cast piece includes a process of supplying molten metal to a molten metal reservoir part formed by a pair of rotary cooling drums 11a, 11b and a pair of side weirs and a process of manufacturing the thin-wall cast piece. Therein, a dummy sheet 7 is inserted between the pair of cooling drums 11a, 11b and is retained when starting casting, the molten metal is supplied to the molten metal reservoir part while rotating the pair of cooling drums 11a, 11b, a non-steady time tfrom a casting starting time to steady casting is set to be five times of solidification time ton a drum circumferential surface upon steady casting or more, and a molten metal supply speed Qat the non-steady time tis set to be twelve times of molten metal supply speed Qupon steady casting or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a thin-walled slab manufacturing method and a thin-walled slab manufacturing apparatus for supplying a molten metal to a molten metal reservoir formed by a pair of cooling drums and a pair of side dams to manufacture a thin-walled slab. It is.

  As a method for producing a thin metal slab, for example, as shown in Patent Document 1, a molten metal is provided in a molten metal pool portion formed between a pair of rotating cooling drums, which includes a cooling drum having a water cooling structure inside. The solidified shells are formed and grown on the peripheral surfaces of the cooling drum, the solidified shells formed on the peripheral surfaces of the pair of cooling drums are joined to each other at the drum kiss point, and pressed to reduce the thickness of the thin casting. A manufacturing method using a twin drum type continuous casting apparatus for manufacturing a piece is provided. The manufacturing method using such a twin drum type continuous casting apparatus is applied to various metals.

  Conventionally, when starting casting in the above-described twin-drum type continuous casting apparatus, for example, as shown in Patent Document 1, a dummy sheet is sandwiched between cooling drums, and a pair of cooling drums and a pair of side weirs are used. Supplying molten metal to the formed molten metal reservoir, rotating the cooling drum when a certain amount of molten metal has accumulated in the molten metal reservoir, and forming a thin slab to connect to the dummy sheet, A dummy sheet and a thin cast piece connected to the dummy sheet are drawn out from between the cooling drums.

Here, since the casting conditions such as the amount of molten metal supplied to the molten metal reservoir and the temperature of the cooling drum are not stable at the start of casting, the thin cast slab formed to be connected to the dummy sheet There was a problem that the strength was insufficient and the thin cast piece was broken when the dummy sheet was pulled out, and casting could not be started.
For this reason, for example, in Patent Document 1, there is a technique for securing the strength of the thin cast piece at the start of casting by arranging a reinforcing member so as to be connected to the dummy sheet and casting the reinforcing member with molten metal. Proposed.

JP 04-266462 A

Here, FIG. 8 shows the relationship between the elapsed time from the start of molten metal supply, the molten metal supply speed, and the drum peripheral speed in the conventional twin-drum type continuous casting method.
In a conventional twin drum type continuous casting apparatus, at the start of casting, a dummy sheet is sandwiched between cooling drums, and the molten metal is supplied in a state where the rotation of the cooling drum is stopped. Then, when a certain amount of molten metal has accumulated, the cooling drum starts to rotate and casting starts. If the molten metal is excessively accumulated between the cooling drums and the solidification becomes excessive, the solidified portion in the molten metal reservoir becomes a wedge, so that the molten metal is conventionally supplied in a relatively short time.

  Immediately after the start of casting, the molten metal stored before rotating the cooling drum is solidified to form an excessive solidified shell. For this reason, immediately after the start of casting, the molten metal supply speed is once decreased and the rotational speed of the cooling drum is gradually increased to discharge the excess, and then the peripheral speed of the cooling drum is gradually increased while the molten metal supply speed is gradually increased. And move to steady casting.

  Here, FIG. 9 shows the relationship between the casting length and the slab thickness in the conventional twin-drum type continuous casting apparatus. Immediately after the start of casting, the molten metal pool portion is solidified to increase the thickness of the slab and form a hump (enlarged portion). Thereafter, due to a decrease in the molten metal supply speed, the thickness of the cast slab is rapidly reduced, and thereafter, the thickness is increased by casting the reinforcing member. In order to withstand the load of the hump (the enlarged portion) formed at the lowermost end, it is necessary to increase the thickness of the slab by the length until this hump (the enlarged portion) moves horizontally.

As described above, when the casting is started by supplying the molten metal in a state where the cooling drum is stopped, the casting time of the unsteady portion becomes long because the time until the steady state is reached, and the yield is increased. There was a problem of a drop.
Moreover, since a hump (enlarged part) is formed at the lowermost end of the slab, the slab is easily broken by its own weight, and there is a possibility that the manufacture of the slab cannot be performed stably.

Furthermore, there is a problem that the length of the reinforcing member necessary for supporting the hump (enlarged portion) formed at the lowermost end of the slab becomes longer and the cost is increased.
Further, when the lowermost hump (the enlarged portion) is crushed and discharged by the cooling drum, the cooling drum may be damaged.
Furthermore, there has been a problem that complicated equipment and control are required for hot-water surface sensing and cooling drum rotation start timing control in a state where the rotation of the cooling drum is stopped.

  The present invention has been made in view of the above-described situation, and the casting length of the unsteady part is short, the fracture of the slab can be suppressed, and the thin-walled slab can be stably manufactured. An object of the present invention is to provide a method for manufacturing a thin-walled slab and an apparatus for manufacturing the thin-walled slab.

In order to solve the above-described problem, a method for manufacturing a thin cast piece according to the present invention supplies molten metal to a molten metal reservoir formed by a pair of rotating cooling drums and a pair of side weirs, A method for producing a thin-walled slab by forming and growing a solidified shell on a peripheral surface to produce a thin-walled slab, wherein a dummy sheet is inserted and held between the pair of cooling drums at the start of casting. The molten metal is supplied to the molten metal pool portion in a state where the cooling drum is rotated, and the unsteady time t _S from the start of casting to the steady casting is determined as the drum during steady casting. It is characterized in that it is 5 times or more of the solidification time t ₀ on the peripheral surface, and the melt supply rate Q _in at the unsteady time t _S is 12 times or less of the melt supply rate Q _ave at the time of steady casting.

According to the method for manufacturing a thin cast piece of this configuration, at the start of casting, a dummy sheet is inserted and held between the pair of cooling drums, and the molten metal pool is rotated while the pair of cooling drums is rotated. Since the said molten metal is supplied with respect to a part, it can suppress that a hump (hypertrophy part) is formed at the time of casting start. Therefore, even if it does not increase the thickness of a thin cast piece, the fracture | rupture of a thin cast piece can be suppressed. Further, the casting length of the unsteady portion can be shortened, and the yield can be improved. Furthermore, it is not necessary to perform hot water surface sensing or rotation activation control, and the equipment configuration can be simplified.
In addition, if a dummy sheet and the cooling drum are in contact after inserting a dummy sheet between the pair of cooling drums, there is a case where a scum enters the cooling drum after the start of casting. It is desirable to hold the pair of cooling drums in a non-contact state.

Further, since the unsteady time t _S from the start of casting to the steady casting is set to be five times or more of the solidification time t ₀ on the drum peripheral surface at the time of steady casting, the molten metal surface in the molten metal pool portion at the start of solidification. As a result, the rate of ascent of the thin slab becomes slow to some extent, a sudden change in the thickness of the thin slab at the unsteady portion can be suppressed, and the thin slab can be prevented from breaking.
Furthermore, since the molten metal supply rate Q _in at the unsteady time ts is 12 times or less than the molten metal supply rate Q _ave at the time of steady casting, it is possible to suppress the molten metal jumping up and the remelting of the solidified shell, and to stably produce a thin-walled slab. Can be cast.

Here, in the method for manufacturing a thin cast piece according to the present invention, it is preferable that at least a part of a space between the dummy sheet, the cooling drum, and the side weir is closed by a sealing member.
In this case, the sealing member can suppress the leakage of the molten metal from the gap between the dummy sheet, the cooling drum, and the side weir, and the casting can be started more stably. In addition, it is preferable to arrange the sealing member so that the sealing member does not rotate with the cooling drum even when the cooling drum is rotated.

  The apparatus for producing a thin cast piece according to the present invention has a pair of rotating cooling drums and a pair of side weirs, and supplies molten metal to a molten metal reservoir formed by the pair of cooling drums and the pair of side weirs. And a thin cast piece manufacturing apparatus for producing a thin cast piece by forming and growing a solidified shell on the peripheral surface of the cooling drum, wherein the dummy sheet holds a dummy sheet downstream of the pair of cooling drums. A holding mechanism is provided, and the dummy sheet holding mechanism holds the dummy sheet inserted between the pair of cooling drums.

  According to the thin-walled slab manufacturing apparatus having this configuration, since the dummy sheet holding mechanism that holds the dummy sheet is provided downstream of the pair of cooling drums, the dummy sheet is inserted between the cooling drums. The cooling drum can be rotated. Therefore, it is possible to start casting by supplying the molten metal to the molten metal pool portion with the cooling drum rotated. Thereby, it can suppress that a hump (expansion part) is formed at the time of a casting start, and even if it does not thicken the thickness of a thin cast piece, the fracture | rupture of a thin cast piece can be suppressed. In addition, the length of the unsteady portion can be shortened, and the yield can be improved. Furthermore, it is not necessary to perform hot water surface sensing or rotation activation control, and the equipment configuration can be simplified.

Here, in the apparatus for manufacturing a thin cast piece according to the present invention, it is preferable that a seal member is disposed on the dummy sheet.
In this case, since the sealing member is disposed on the dummy sheet, the gap between the dummy sheet, the cooling drum, and the side dam can be reduced by the sealing member, so that the molten metal can be prevented from leaking, and casting can be further performed. It becomes possible to start stably. In addition, since the sealing member is arrange | positioned at the dummy sheet | seat, even if the cooling drum is rotated, it can suppress that a sealing member rotates with a cooling drum.

  As described above, according to the present invention, the method for producing a thin-walled slab is capable of stably producing a thin-walled slab, in which the casting length of the unsteady portion is short and the slab can be prevented from breaking. And the manufacturing apparatus of a thin wall slab can be provided.

It is explanatory drawing which shows the manufacturing apparatus of the thin cast slab which is embodiment of this invention. In the apparatus for manufacturing a thin cast piece shown in FIG. 1, (a) a state in which a dummy sheet is held at the start of casting and (b) a state after the start of casting. It is explanatory drawing which looked at the arrangement | positioning of a dummy sheet from the upper direction of the cooling drum. In a dummy sheet holding | maintenance apparatus, (a) The state which hold | maintained the dummy sheet at the time of casting start, (b) It is explanatory drawing which shows the state after the casting start. It is explanatory drawing of the parameter used when determining the molten metal supply conditions at the time of a casting start. It is a graph which shows the relationship between the elapsed time from the casting start in the manufacturing method of the thin cast slab which is embodiment of this invention, and a molten metal volume velocity. It is a graph which shows the relationship between the casting length from the casting start in the manufacturing method of the thin cast slab which is embodiment of this invention, and slab thickness. It is a graph which shows the relationship between the elapsed time from the molten metal supply start in the conventional twin drum type continuous casting method, and a molten metal supply speed | rate. It is a graph which shows the relationship between the casting length from the casting start in the conventional twin drum type continuous casting method, and slab thickness.

Below, the manufacturing method of the thin cast slab and the manufacturing apparatus of a thin cast slab which are embodiments of the present invention are explained with reference to the attached drawings. In addition, this invention is not limited to the following embodiment.
Further, in the present embodiment, molten steel is used as the molten metal, and the thin cast slab 1 made of a steel material is manufactured.

  As shown in FIG. 1, the thin-walled slab manufacturing apparatus 10 according to the present embodiment includes a pair of cooling drums 11 a and 11 b and side weirs 15 disposed at widthwise ends of the pair of cooling drums 11 a and 11 b. And a tundish 18 and an immersion nozzle 19 for supplying the molten steel 3 to the molten steel pool 16 defined by the pair of cooling drums 11 a and 11 b and the side weir 15.

  In this thin cast piece manufacturing apparatus 10, the solidified shells 5 and 5 grow on the peripheral surfaces of the cooling drums 11a and 11b by cooling the molten steel 3 in contact with the rotating cooling drums 11a and 11b. Then, the solidified shells 5 and 5 formed on the pair of cooling drums 11a and 11b are pressure-bonded at the drum kiss point, whereby the thin cast piece 1 having a predetermined thickness is cast.

  In the thin-walled slab manufacturing apparatus 10 according to the present embodiment, as shown in FIG. 2, when casting is started on the downstream side of the pair of cooling drums 11 a and 11 b, the pair of cooling drums 11 a and 11 b A dummy sheet holding mechanism 20 that holds the dummy sheet 7 inserted therebetween is provided. As shown in FIG. 2A, a reinforcing member 9 that is cast into the thin cast piece 1 is disposed on the upper end side of the dummy sheet 7.

  Here, at the start of casting, as shown in FIGS. 2A and 3, the dummy sheet 7 is inserted between the pair of cooling drums 11 a and 11 b, and the dummy sheet 7 is moved by the above-described dummy sheet holding mechanism 20. Retained. In the present embodiment, the dummy sheet 7 is held by the dummy sheet holding mechanism 20 in a non-contact state with respect to the pair of cooling drums 11a and 11b. The cooling drums 11a and 11b are provided with an initial concave crown in which the outer diameter of the central portion of the drum width is reduced in consideration of thermal expansion, and a dummy sheet is formed in the drum gap formed by the concave crowns. 7 is inserted.

  Further, the dummy sheet 7 is provided with a seal member 8, and at least a part of the space between the dummy sheet 7 and the cooling drums 11 a and 11 b and the side weir 15 is blocked by the seal member 8. Yes. In addition, as the sealing member 8, the soft material which has heat resistance, such as a refractory fiber material, can be used.

As shown in FIGS. 2 and 4, the dummy sheet holding mechanism 20 has an arm portion 21, a roll portion 22 disposed on one end side of the arm portion 21, and the other end side of the arm portion 21 as an axis. A shaft support portion 23 to be supported and a pressing means 24 (plate spring) for pressing the shaft support portion 23 toward one end side of the arm portion 21 are provided.
In this dummy sheet holding mechanism 20, as shown in FIG. 4A, when holding the dummy sheet 7, the roll portion 22 is pressed against one end side of the arm portion 21 by the pressing means 24, and the roll The dummy sheet 7 is sandwiched by the portion 22.
When the dummy sheet 7 is pulled out downward, as shown in FIG. 4B, the roll portion 22 moves downward to release the dummy sheet 7.

  Below, the manufacturing method of the thin cast piece which is this embodiment using the manufacturing apparatus 10 of the thin cast piece mentioned above is demonstrated.

  First, as shown in FIGS. 2A and 3, the dummy sheet 7 is inserted between the pair of cooling drums 11a and 11b from the downstream side of the pair of cooling drums 11a and 11b. At this time, the dummy sheet holding mechanism 20 holds and holds the dummy sheet 7. In the present embodiment, the dummy sheet 7 is held in a non-contact state with respect to the cooling drums 11a and 11b. Here, at least a part of the space between the dummy sheet 7 and the cooling drums 11 a and 11 b and the side weir 15 is closed by the sealing member 8 disposed on the dummy sheet 7.

And a pair of cooling drum 11a, 11b is rotationally driven. At this time, the dummy sheet is held by the dummy sheet holding mechanism 20, and in this embodiment, the dummy sheet is held in a non-contact state with the cooling drums 11a and 11b, and the sealing member 8 is cooled by the cooling drums 11a and 11b. Since the sliding drum 11a and 11b are rotated, the dummy sheet 7 and the seal member 8 are not caught between the pair of cooling drums 11a and 11b. .
In the present embodiment, the rotational speeds (circumferential speeds) of the cooling drums 11a and 11b are set to be the same as the rotational speeds (circumferential speeds) during steady casting.

In a state where the cooling drums 11a and 11b are rotated, the molten steel 3 is supplied from the tundish 18 through the immersion nozzle 19 toward the molten steel pool portion 16 formed by the pair of cooling drums 11a and 11b and the side weir 15. .
Then, when the molten steel 3 is solidified so as to enclose the reinforcing member 9, the dummy sheet 7 is discharged downward so as to be wound around the rotating cooling drums 11 a and 11 b, and the thin cast 1 Is discharged.
Here, when the dummy sheet 7 is discharged downward, as shown in FIGS. 2B and 4B, the roll portion 22 of the dummy sheet holding mechanism 20 moves downward, and the dummy sheet 7 is moved downward. Is released.

And when the molten metal surface height in the molten steel pool part 16 is stabilized at a predetermined position, solidification is stabilized and steady casting is performed.
Here, in the present embodiment, the unsteady time t _S from the start of casting to the steady casting is set to 5 times or more of the solidification time t ₀ on the drum peripheral surface at the steady casting.
Further, the melt supply rate Q _in at the unsteady time ts is set to 12 times or less of the melt supply rate Q _ave at the time of steady casting.
The reason why the conditions at the start of casting are defined as described above will be described below.

FIG. 5 shows parameters used when setting conditions at the start of casting. The supply speed (molten volume speed) of the molten steel 3 supplied to the molten steel pool portion 16 is Q _in , and the discharge speed (molten volume speed) of the molten steel 3 corresponding to the thin cast slab 1 discharged from between the cooling drums 11a and 11b. ) Is Q _out , the molten steel surface height (height from the drum center position) in the molten steel pool 16 is H, the arc angle of the contact portion of the molten steel 3 on the drum peripheral surface is θ, and the thickness of the thin cast slab 1 is d And From the arc angle θ and the drum radius R, the contact length L of the molten steel on the drum peripheral surface can be calculated.
Further, K is a solidification coefficient indicating the amount of solidification per unit time. The solidification coefficient K is set according to the composition of the thin cast slab and the cooling conditions, and can be experimentally obtained in advance.

FIG. 6 shows the relationship between the elapsed time from the start of casting and the molten metal volume velocity in the method for producing a thin cast slab which is an embodiment of the present invention.
After the start of casting, the molten steel supply rate Q _in is made higher than the molten metal discharge rate Q _out, whereby the molten steel 3 is stored in the molten steel pool portion 16 and the molten metal surface height H is increased. That is, the hot water surface height H rises according to Q _in -Q _out .

As the molten metal surface height H increases, the solidification length L on the circumferential surface of the cooling drum increases, and the solidification thickness, that is, the thickness d of the thin cast slab 1 increases, and the molten metal discharge speed Q as shown in FIG. _out gradually rises.
On the other hand, the molten metal supply rate Qin gradually decreases with time, and when the unsteady time t _S ends and the steady casting is performed, Q _in = Q _out , which is the molten metal supply rate in the steady state. Q _ave .
In FIG. 6, the difference between Q _in and Q _out at the unsteady time t _S is the amount of molten steel stored in the molten steel pool 16.

Here, let V be the peripheral speed of the cooling drums 11a and 11b. Then, the molten metal discharge rate Q _out is determined by the product of the thickness d and the drum peripheral speed V and the slab width W of the thin slab 1. The thickness d of the thin cast slab 1 is calculated by the following formula using the molten metal surface height H, the solidification coefficient K, and the drum radius R.
d = 2 × K × (R × arcsin (H / R) / V) ^0.5

The melt feeding rate Q _in, immediately after the start of casting is rapidly raise the melt-surface height H, in order to gradually increase the melt-surface height H toward the predetermined height, the melt feeding rate Q _in time As shown in FIG. 6, the change pattern is preferably convex downward so as to be a quadratic function of time, for example.

Here, if setting a low melt feeding rate Q _in, the height H is gradually increased molten metal surface, the time to steady state becomes longer. Conversely, by setting the molten metal supply rate Q _in high, the time until the molten metal surface height H is set to a predetermined height can be shortened. However, even if it is instantaneous, if it is supplied excessively vigorously, the molten steel springs up and the solidified shell remelts, and the casting may become unstable. The maximum value of the molten metal supply rate Q _in is influenced by the apparatus size, the molten metal surface height H, the molten metal type, and the like, but normally it may be 12 times or less of the molten metal supply rate Q _ave in the steady state.

Further, by shortening the unsteady time t _S, it is possible to shorten the casting length of the non-stationary portion. However, if the unsteady time t _S is too short, the upper limit of the molten metal supply rate Q _in may be exceeded, which is not preferable. Alternatively, when the unsteady time t _S becomes less than 5 times the steady solidification time t ₀ = (d / 2K) ^0.5 calculated from the solidification coefficient K and the thickness d of the thin-walled slab 1 at the steady time, the molten steel The rate of change of the molten metal surface height H in the pool portion 16 is increased, and accordingly, the thickness of the thin cast piece 1 in the unsteady portion is rapidly changed from thin to thick in the casting length direction. There is a possibility that stress concentrates on a thin portion of the plate 1 during the conveyance of the piece 1 and breaks. In order to prevent these, the unsteady time t _{S is set} to be five times or more of the solidification time t ₀ on the drum peripheral surface during steady casting. Further, if the unsteady time t _S is long, the casting length of the unsteady portion of the slab becomes long and the yield tends to decrease. Therefore, the unsteady time t _S is the solidification time on the drum peripheral surface during steady casting. 15 times of t ₀ or less is desirable.

The molten metal supply rate Q _in and the unsteady time t _S are set so as to satisfy the above requirements. These conditions may be obtained by a numerical analysis simulation or may be obtained experimentally. FIG. 7 shows a solidification coefficient K = 14.0, a drum radius R = 0.3 m, a drum peripheral speed V = 50 m / min, a thickness d = 2 mm of the thin slab 1 using 0.1% carbon steel, Molten surface height h = 230 mm, unsteady time t _S = 2.3 s (7.3 times the steady solidification time t ₀ ), molten metal supply speed Q _in = 1.16 m ³ / min (molten metal supply speed during steady casting) An example of the change in thickness of the thin cast slab 1 at 11.7 times Q _ave ) is shown.

  As shown in FIG. 7, even at the start of casting, the thickness d of the thin cast slab 1 does not vary greatly, and no humps (enlarged portions) are formed. Furthermore, it is in a steady state quickly, and the casting length of the unsteady part is shortened.

  According to the thin-walled slab manufacturing apparatus 10 and the thin-walled slab manufacturing method according to the present embodiment configured as described above, the pair of cooling drums 11a and 11b are rotated at the start of casting, Since the molten steel 3 is supplied to the molten steel pool portion 16, it is possible to suppress the formation of a hump (enlarged portion) at the start of casting, and the thin cast slab can be obtained without increasing the thickness of the thin cast slab 1. 1 breakage can be suppressed. In addition, the length of the unsteady portion can be shortened, and the yield can be improved. Furthermore, it is not necessary to perform hot water surface sensing or rotation activation control, and the equipment configuration can be simplified.

Further, since the unsteady time t _S from the start of casting to the steady casting is set to be 5 times or more of the steady solidification time t ₀ , the rising speed of the molten metal surface in the molten steel pool portion 16 becomes somewhat slow at the start of solidification, An abrupt change in the thickness of the thin cast 1 at the unsteady portion can be suppressed, and breakage of the thin cast 1 can be suppressed.
Furthermore, since the molten metal supply rate Q _in at the unsteady time ts is set to 12 times or less of the molten metal supply rate Q _ave at the time of steady casting, it is possible to suppress the jumping of the molten steel 3 and the remelting of the solidified shell, and stably perform the thin wall casting. The piece 1 can be cast.

As mentioned above, although the manufacturing method of the thin cast slab and the thin cast slab manufacturing apparatus 10 which are the embodiments of the present invention have been specifically described, the present invention is not limited to this, and the technical idea of the present invention is not limited thereto. Changes can be made as appropriate without departing from the scope.
In the present embodiment, the rotation speed (circumferential speed) of the cooling drums 11a and 11b has been described as being set to be the same as the rotation speed (circumferential speed) at the time of steady casting, but the present invention is not limited to this. The rotation speed (circumferential speed) of the cooling drums 11a and 11b at the start may be changed as appropriate.

In the present embodiment, the molten metal supply rate Q _in at the start of casting has been described as being convex downward so as to be a quadratic function of time, for example, as shown in FIG. If the upper limit of the molten metal supply rate Q _in at the start of casting is 12 times or less of the molten steel supply rate Q _ave at the time of steady casting, the molten metal supply rate Q _in at the start of casting is changed to another pattern. It may be changed with.

In the following, the results of experiments conducted to confirm the effects of the present invention will be described.
Using the apparatus for manufacturing a thin cast piece shown in FIG. 1, a thin cast piece made of carbon steel having a carbon content of 0.1 mass% was produced.
Here, the cooling drum diameter was 600 mm, and the cooling drum width was 1000 mm. The slab thickness for steady casting was 2.0 mm.

In the present invention example and the comparative example, as shown in the above-described embodiment of the present invention, at the start of casting, the dummy sheet is held in a non-contact state with the cooling drum, and the cooling drum is rotated. Molten steel was supplied to the molten steel pool. Table 1 shows the conditions at this time.
Further, in the conventional example, at the start of casting, the dummy sheet is sandwiched between the cooling drums, and the molten steel is supplied to the molten steel pool portion while the cooling drum is stopped.

  At this time, the casting length of the unsteady part and the fluctuation width of the slab thickness in the unsteady part were evaluated. The evaluation results are shown in Table 1.

In the conventional example, the fluctuation of the slab thickness is large, and the slab may be broken. Moreover, the casting length of the unsteady part was long and the production yield was low.
In Comparative Example 1, the unsteady time t _S is less than five times the solidification time t ₀ on the drum peripheral surface during steady casting, and the rate of change in the slab thickness in the casting length direction is large. A break occurred when the piece was transported from the drum.
In Comparative Example 2, the melt supply rate Q _{in at the} unsteady time t _S exceeds 12 times the melt supply rate Q _ave at the time of steady casting, and solidification is not stabilized due to the jumping of molten steel or remelting of the solidified shell. The slab broke.

  On the other hand, in the examples of the present invention, fluctuations in the slab thickness were all kept small, and the casting length of the unsteady portion could be shortened as compared with the conventional example.

  From the above results, according to the thin-walled slab manufacturing method and thin-walled slab manufacturing apparatus according to the present invention, the thin-walled slab manufacturing method and thin-walled slab can be stably cast with a high yield. It was confirmed that the manufacturing equipment can be provided.

1 Thin-walled slab 3 Molten steel (molten metal)
5 Solidified shell 7 Dummy sheet 8 Seal member 10 Thin-walled slab manufacturing apparatus 11a One cooling drum 11b The other cooling drum 16 Molten steel reservoir (molten metal reservoir)
20 Dummy sheet holding mechanism

Claims (4)

Thin-walled slab for supplying a molten metal to a molten-metal reservoir formed by a pair of rotating cooling drums and a pair of side weirs, and forming and growing a solidified shell on the peripheral surface of the cooling drum to produce a thin-walled slab A manufacturing method of
At the start of casting, a dummy sheet is inserted and held between the pair of cooling drums, and the molten metal is supplied to the molten metal pool portion with the pair of cooling drums rotated. And
The unsteady time t _S from the start of casting to the steady casting is set to 5 times or more of the solidification time t ₀ on the drum peripheral surface during the steady casting,
A method for producing a thin-walled cast slab, characterized _in that the molten metal supply rate Q _in at the unsteady time t _S is 12 times or less of the molten metal supply rate Q _ave at the time of steady casting.   The method for producing a thin slab according to claim 1, wherein at least a part of a space between the dummy sheet, the cooling drum, and the side weir is closed by a sealing member. A pair of rotating cooling drums and a pair of side weirs are provided. Molten metal is supplied to a molten metal reservoir formed by the pair of cooling drums and the pair of side weirs, and a solidified shell is provided on the peripheral surface of the cooling drum. A thin-walled slab manufacturing device for producing and growing thin-walled slabs,
A dummy sheet holding mechanism for holding a dummy sheet is provided on the downstream side of the pair of cooling drums,
The apparatus for producing a thin-walled slab, wherein the dummy sheet holding mechanism holds the dummy sheet inserted between the pair of cooling drums.   The apparatus for producing a thin cast piece according to claim 3, wherein a seal member is disposed on the dummy sheet.

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