JPS62244554A - Continuous casting method for casting sheet - Google Patents

Abstract

PURPOSE:To prevent the breakdown and the burning of initial solidified shell by drawing as casting a casting sheet from molten metal between circulating bodies arranged as facing and changing periodically rotary shifting speed for the above circulating bodies and drawing speed for the casting sheet. CONSTITUTION:The molten metal 15 supplied from a pouring nozzle 9 is poured into the space forming between one pair of endless belts 1, which are arranged as facing and cools their back faces by water film cooling box 6 and are rotately shifted by rolls 4, 7, 8, and the fixed side face cooling bodies (no shown in the figure) arranged as facing, through molten metal supply nozzle 9, and the casting sheet 12 is produced by continuous casting and drawn by pinch rolls 2. In the above method, the rotary shifting speed of the above endless belt 1 and drawing speed of the casting sheet 12 are periodically changed as synchronizing or as independent. In this way, the breakdown of the initial solidified shell and the burning to the above fixed side face cooling bodies are prevented and the occurrence of breakout is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to the field of preventing an initially solidified shell from breaking or seizing on a fixed side cooling body during continuous casting of a thin slab.

(Prior Art) Conventionally, a pair of movable belts are disposed opposite to each other and circulate while maintaining a gap for holding molten metal over a certain distance, and movable belts are disposed opposite to each other on both side edges of the movable belts. A casting method has been proposed in which molten metal is supplied into a space formed by a fixed side cooling body from a molten metal supply nozzle that comes into contact with the fixed side cooling body. However, in this method, since the fixed side cooling body is fixed, the tensile strength of the initial solidified shell formed on the fixed side cooling body is greater than the frictional force between this shell and the fixed side cooling body. If the shell becomes smaller, it will break and become lodged on the fixed side cooling body, leading to a breakout if it is cast as is. Such a breakout is generally called a restricted breakout, and the breakout occurs through the stages shown in FIG. In other words, the thinnest shell 17 is formed between the shell 16 that is stationary on the fixed side cooling body and the shell 18 that is moving. If the shell 16 staying on the fixed side cooling body moves together with the shell 18 moving away from the fixed side cooling body before this shell 17 moves to the exit side of the fixed side cooling body 14, the first It is possible to cast continuously as shown in the figure. However, the shell 16 stuck on the fixed side cooling body
If the molten steel 15 does not separate from the fixed side cooling body, as shown in FIG. 1b, the molten steel 15 leaks from the outlet side of the fixed side cooling body 14, and a so-called restraint breakout occurs. Furthermore, a similar phenomenon occurs when a solidified shell is baked onto the fixed side cooling body.

Therefore, as a technique for preventing breakout caused by the solidified shell being baked into the fixed side cooling body, support cooling members corresponding to the fixed side cooling body of the present invention are arranged at both side edges of a pair of opposing endless belts. Japanese Unexamined Patent Application Publication No. 153553/1983 proposes applying slight vibrations to the cooling member to prevent the solidified shell from seizing on the supporting cooling member.

In addition, in a continuous metal casting apparatus having a moving mold, it is particularly desirable to prevent the moving mold from sticking to the solidified shell by setting the moving speed of the mold to a constant speed that is higher than the fixed slab moving speed. This is proposed in Japanese Patent Publication No. 56-165543.

(An unsuccessful means to solve the problem) However, since the former technique described above has a structure in which the molten metal supply nozzle is in contact with the support cooling member, when slight vibrations are applied, the molten metal supply nozzle and the support cooling member There were cases where a gap was formed between the molten metal and the tip of the molten metal supply nozzle, and the tip of the molten metal supply nozzle was damaged. For this reason, there is a problem that the surface quality of the slab deteriorates or breakout occurs due to the molten metal being inserted into this part, which causes slight vibrations to the fixed side cooling body of JP-A-59-153553. Technology cannot be applied.

In addition, in the latter technology, the initially solidified shell cooled and solidified by the endless belt is pulled out at a constant speed, and the shell is pulled out in synchronization with the endless belt and is cooled and solidified on the fixed side cooling body and stagnates. Sliding friction occurs at the boundary between the shell and the shell.

This sliding friction force pulls the shell stuck on the stationary side cooling body away from the stationary side cooling body, but since this phenomenon is not constant, there is a risk of breakout.

(Means for Solving the Problems) The present invention produces thin slabs using a continuous casting machine having a structure in which a molten metal supply nozzle contacts a fixed side cooling body as shown in FIGS. 3, 4, and 5. The above problem was solved by periodically changing the thin slab drawing speed Vc and the rotational movement speed ν8 of the pair of endless belts or one of the endless belts during continuous casting.

Further, as a mode of periodically changing the drawing speed VC of the thin slab and the rotational movement speed VB of the endless belt, the second method is as follows.
As shown on the right side of Figure A and Figure 2B, the waveform of the rotational movement speed of the endless belt and the waveform of the drawing speed of the thin slab are made to match,
Also included is a mode in which the speeds at each instant are matched.

The electrical means for periodically changing the rotational movement speed VB of the endless belt and the drawing speed Vc of the thin slab mentioned above include constantly detecting each speed and adjusting the preset period 1/f.
(f is the frequency> and amplitude a1 and pulse width l]
Control the rotational speed of the endless belt and pinch roll drive motor to match. Figure 2a and Figure 2 [1]
As a result of experiments, the drawing speed of the thin slab shown in the figure, Vc, and the period 1/f of the rotational movement speed, VB, of the endless Peruvian shell were determined to be V, the drawing speed of the initially solidified shell. , Ic, which is equal to the length of the fixed side cooling body, and the pitch per cycle is , , then O<L
h (mm/c), that is, the periodicity is such that the pitch at which the initially solidified shell is intermittently pulled out by one endless belt and the periodic speed of thin slab drawing speed is greater than Q+++m and less than the fixed side cooling length. 1/fυ, good.

Further, as shown in FIG. 2C, the rotational movement speed VB of the endless belt and the drawing speed ν of the thin slab. Even when changing periodically, the period 1/f1 and amplitude a1 of the rotational movement speed VB of the endless belt and the period 1/f2 of the drawing speed Vc of the thin slab
The amplitude a2 may be given in the same manner as in FIG. 2a, but preferably 1/f2<1/f2.

(Function) The method of the present invention is based on the rotational movement speed Vn of the endless belt and the slab drawing speed V. By periodically changing the sliding friction force, the sliding friction force can be changed periodically in response to the periodic velocity changes, and the initially solidified shell stagnant on the fixed side cooling body is periodically separated. becomes possible.

In addition, the periodic speed changes in the rotational movement speed of the endless belt and the slab withdrawal speed give vibration to the initially solidified shell, so that the molten metal supply nozzle and the fixed side cooling body that are in contact with the fixed side cooling body have almost no vibration. Vibrations are not propagated.

(Example 1) The molten metal from the injection nozzle 9 is rotated through the molten metal holding container 5 and the molten metal supply nozzle 3 by the drive roll 8, the tension roll 7, and the inlet roll 4, and the back side is cooled by the water film cooling box 6. Endless belt 1 and length 30 (not shown)
The molten metal 15 is placed in the space formed by the fixed side cooling body of 0 mm.
Figure 3 shows an apparatus for injecting . Using this device, a thin slab (SS41) with a thickness of 20 mm and a width of 600 mm is pulled out at an average slab drawing speed v0 of 5 m/min, and the rotational movement speed VB of the endless belt below and the drawing of the initial solidified shell are Speed V.

asin2 with vo as the reference as shown in Figure 1a.
Casting was performed by periodically varying the amount of πft.

Note that a at this time is 0.3 m/min, and f is 6
It was set to 0 times/min.

(Example 2) The average slab drawing speed (V
o) Pulled out at 7m/min. At this time, the rotational movement speed vB of the endless belt and the drawing speed V of the initially solidified shell. with the pattern shown in Figure 2b, a is 0.5m/mi
n and b were set to 0.2 to 0.3 seconds, and r was set to 60 times/min.

(Example 3) A thin slab (spc) with a thickness of 10 mm and a width fi [10 mm
c) ν. = 10m/min, average value of VB 11m
/min, f, = 60 times/min, f2 = 30 times/
min, a,=Q, 3Qm/min, a2=Q
, 15 m/min, L = 450. For comparison, Table 1 shows the results of casting with the drawing speed and the rotational movement speed of the endless belt constant as in the conventional case.

As you can see from this table, the complete casting rate ranges from 43% to 100%.
%, the surface of the slab is beautiful, and although some rub marks can be seen on the sides of the slab due to the periodic speed changes of the endless belt, the shell has a fixed side rotational movement speed vn, and the initial solidified shell is pulled out. Speed Vc and average slab drawing speed V. Figures 3, 4 and 5 are diagrams showing the apparatus used in the method of the present invention.

1...mt End held 2...Pinch roll 3...
Molten metal supply nozzle 4...Inlet roll 5...Molten metal holding container 6...Water film cooling box 7...Dension roll End...Drive roll 9...Injection nozzle 1
0...Inert gas population 11...Atmosphere adjustment cover
12...Thin slab 13...Bending roll 14.
... Fixed side cooling body 15 ... Molten metal 16 ... Stagnant shell 17 ... Thin shell 18 ... Moving shell)

Claims (1)

[Claims] 1. A pair of circulating bodies disposed opposite to each other that circulate while maintaining a gap to hold the molten metal over a certain distance;
The molten metal is supplied from the molten metal supply nozzle that is in contact with the fixed side cooling bodies into the space formed by the fixed side cooling bodies placed opposite to both side edges of the circulation body to continuously form thin slabs. A continuous casting method for thin slabs, characterized in that casting is carried out while periodically changing the rotational movement speed of the circulating body and the drawing speed of the slabs to be drawn. 2. Continuation of thin slabs according to claim 1, characterized in that the waveform of the rotational movement speed of the circulating body and the waveform of the withdrawal speed of the slab are matched, and the respective speeds at each instant are made to match. Casting method.