JPS6040660A - Continuous casting device of thin-walled slab - Google Patents

Abstract

PURPOSE:To provide a titled device which casts continuously a thin-walled slab irrespectively of the size of a nozzle tip of oscillating mold and synchronously moving belt type continuous casting by providing a servocontrol nozzle in the upper part of the casting mold which oscillates finely at a high cycle thereby narrowing the mold space. CONSTITUTION:The molten steel in a tundish 1 is received by an immersion nozzle 2 into a servocontrol nozzle body 3 on a mold 5 which oscillates finely and vertically at a high cycle and is poured and sagged into the mold 5 through the narrow nozzle gap corresponding to the thin wall thickness. The molten steel is continuously cast and sagged by the narrow gap irrespectively of the size of the nozzle 2 and therefore the inside of the mold 5 is kept free from undue stress. Since the molten steel is smoothly sagged by fine oscillation without rippled surface, the satisfactory thin-walled slab is obtd.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a continuous thin-walled slab casting apparatus for manufacturing thin-walled slabs of steel materials, etc., and in particular improves the mold and its vibration structure,
The present invention relates to a continuous thin slab casting apparatus suitable for continuous casting of thin slabs with smooth slab surfaces.

[Background of the invention]

Conventionally, a vibrating mold is installed in the slab drawing direction, and a belt-type mold is installed continuously on the downstream side of the vibrating mold and moves in synchronization with the slab. Molten metal is poured from a tundish into the vibrating mold to continuously form a slab. Continuous slab casting equipment is known that allows continuous slab casting.

In addition, in the past, the vibration frequency of the vibrating mold was generally about 1100.
It is said to be cp. Then, the slab shaped by this vibrating mold is passed through guide rolls, and while suppressing the bulging caused by the static pressure of the molten steel, the slab is cooled with water supplied from the roll gap through a spray nozzle, and solidification progresses. That's what I do.

However, 0.2 to 0.5.0 bulging may occur in the portion of the slab that is not supported by the guide rolls, and cracks may occur inside the slab.

Therefore, in order to prevent bulging, various countermeasures have been considered in the past. For example, in Japanese Patent Application No. 54531/1987, a belt that moves in synchronization with the slab instead of the guide roll and a cooling pad that supports and cools the belt are used. A technique has been disclosed that adopts a belt guide force type. This method is characterized by the fact that, in principle, no lugging strain occurs because the slab can be supported continuously until the completion of solidification.

However, with this belt guide method, secondary cooling of the slab is performed indirectly via the belt tracker, so
If the surface of the slab is smooth, sufficient cooling and uniform cooling will be possible, but depending on the vibration mold that was actually used, the surface of the slab may have a depth of 0.3 to 0.5 mm, and a thickness of 15 mm and 1 liter.
Since there are oscillation marks and the surface unevenness is extremely bad, the belt guide part is strongly cooled while the concave part is not easily cooled, resulting in uneven cooling and the slab is broken at the boundary between the convexity and convexity. The disadvantage is that surface cracks occur.

Therefore, this belt guide method has not been put into practical use.

On the other hand, for shaping small-width slabs, various belt-synchronous continuous casting machines that enable high-speed casting have been proposed in place of the above-mentioned vibrating molds, and some of them have been put into practical use. This ensures a smooth surface without any V-john marks and increases speed (10
m/I'd"). However, in the case of wide cross-section materials such as slab materials, the
Because it is necessary to use a wide belt, when directly supporting and cooling the molten steel, only the area in contact with the molten steel increases in temperature (approximately 250 tr).
), and since the non-contact parts at both ends of the belt are close to room temperature, thermal expansion in the center of the belt causes gentle unevenness in the belt at the molten steel support part (deterioration of the shape of a flat belt), which causes the slab to Since the molding process involves molding, there is a drawback that a slab material with irregularities is cast.

As mentioned above, both the conventional vibrating mold and belt guide combination method and the belt synchronous continuous casting machine have the drawback that the surface quality of the slab is unstable, and further improvements are desired for practical use. was.

Incidentally, in recent years, in order to save energy, there has been a desire to connect continuous casting and hot rolling, and to realize direct rolling that does not require reheating of slabs. In addition, the conventional large cross-section slab (thickness 250 to 300 mm) was thinned and rough rolled (2
Efforts are also being made to omit the process of rolling from 50 m to 300 m thick to 60 m to 30 m thick. However, to achieve this, the hot finish rolling capacity (approximately 50 Q ton/) (
It is necessary to develop a high-speed casting machine for thin-walled slabs commensurate with r ), but currently the maximum slab thickness H is about 80 TIaR.

The reason for this is that it is difficult to reduce the outer diameter of the immersion nozzle that pours into the mold to 40 to 50 mm or less for strength and manufacturing reasons, and the gap G on one side between the mold and the immersion nozzle is also 15 to 2 mm.
This is because if it is not set to 0 rMn or more, the molten steel will solidify in this part, and the immersion nozzle will be drawn into the solidified slab and break, making it difficult to continue the operation. That is, in order to operate stably, it was necessary to satisfy H≧D+2G=50+2X15=80 gourds.

As described above, it has been difficult to form thin slabs of 30 to 60+ m, which are required in recent years, with conventional continuous casting equipment.

[Purpose of the invention]

An object of the present invention is to provide a continuous thin-walled slab casting apparatus that enables direct casting of FC thin-walled and smooth-surfaced slabs, which has been difficult in the past.

[Summary of the invention]

In order to achieve the above object, the continuous thin slab casting apparatus according to the present invention includes a vibrating mold that vibrates in the slab drawing direction, and a belt type mold that is continuously provided downstream of the vibrating mold and moves in synchronization with the mold. The vibrating mold is vibrated slightly at a high cycle, and a servo nozzle is directly connected to the upper part of the vibrating mold to maintain a constant level of the molten metal.

First, the present invention will be discussed theoretically.

(Improvement of surface quality) In the present invention, by making the vibrating mold vibrate at high cycles, it is possible to significantly reduce the depth and pitch of wrinkles. That is, oscillation marks generally occur at the following pitch.

Assuming that the mold frequency is N1 and the casting speed is V, the pitch fP of the oscillation mark is generated according to the formula P=V/N (1). The depth δ of hot water wrinkles has a relationship of δσPαv/N. Therefore, if δ and P'ft are made smaller, the surface of the slab can be made smoother, so in the end, it is sufficient to make V/Ne smaller. For example, in the conventional vibration mold, actual measurement δ = 0.5 van (δ/P = 0.033)
When an object with such onation marks is supported by a belt, the protrusion of the mark comes into contact with the belt, but a gap is created between the other parts and the belt.

in this case The thermal conductivity is It is small and has insufficient cooling.

In reality, α=250 km/mh deg is required, so it was found that δ needs to be 0.5/2.5=0.2 mm or less.

Therefore, when V is constant with high cycle (soocpm) micro vibration, δ = 0.033 Q
When QQm/-, δ=0.033X3=0.1m+n. Even in high-speed casting, a smooth surface can be obtained by applying a microvibration of 5000 cpm.

Another factor that deteriorates surface quality is fluctuations in the molten metal level within the mold. To suppress this, the hot water level position is generally detected and controlled to be constant (fry pan flow rate control or drawing speed control), but the control limit is usually ±3 degrees.

The reason why wrinkles occur due to fluctuations in the hot water level is thought to occur because the shell that begins to solidify near the hot water surface solidifies and shrinks, falls inside the mold, and the hot water level rises to cover it. In other words, it is thought that this will not occur if the fluid level fluctuation is zero. Therefore, in the present invention, the hot water level is positioned above the solidification start position, and the servo nozzle is used to prevent the occurrence of wrinkles due to fluctuations in the hot water level.

■(High-speed casting) Slabs with smooth surfaces can be manufactured by using the above-mentioned high-cycle microvibration and subsurface solidification method, but the casting speed is 1.
．． 5 to 2.0 m/-, the slab pulling force is
Since the exit side of the mold has a sufficient solidification thickness (approximately 10 van ), the solidification shell ruptures (so-called B).

0) is unlikely to occur, so it can be adopted without any problem.

However, the length of the vibrating mold is the same as the conventional one (approximately 800 mm).
When high-speed casting is performed as described in (2), the shell thickness on the exit side of the mold does not grow sufficiently, so the solidified shell breaks.

Furthermore, if the length of the mold is increased in order to increase the thickness of the shell, the pull-out resistance will increase, and eventually the solidified shell will break on the exit side of the mold. That is, when increasing the speed, there is a limit to the length of the vibrating mold, and it is impossible to increase the length beyond this limit. Such a relationship is shown in FIG.

In other words, at low speeds it is sufficiently long (2.0 m/-).
m) is possible, but if V=15m/-high speed, it is necessary to set LM≦600m.

Therefore, by adopting a double-belt mold of the slab synchronization type for subsequent molds, it is possible to compensate for the long-lasting point.

Furthermore, by using a belt guide system for the downstream section, as shown in Figure 2, the temperature rise of the belt can be halved compared to the conventional belt hook system, which prevents defects in shape due to thermal expansion of the belt and creates a smooth and smooth surface. It is possible to secure the slab surface. Also,
In the high-cycle micro-vibration mold, a slab with a smooth surface is formed, so the contact state between the belt and the slab surface is uniform, uniform surface cooling is possible, and there are no surface cracks caused by unevenness. be.

(Thin-walled slab modeling) Due to the limitations of pouring thin-walled slabs, the currently possible thickness is 80 mm or more, as mentioned above. The present invention enables thin-wall casting by directly connecting a servo nozzle to the upper part of a micro-vibration mold.

Since this servo nozzle begins receiving molten steel in a sufficiently preheated state to prevent the molten steel from solidifying, it also has the function of preventing the occurrence of wrinkles due to the below-the-surface solidification method, as described above.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 to 5.

The flow rate of the molten steel in the tandic unit from the immersion nozzle 2 is controlled to be almost constant. A ceramic nozzle 4 whose opening size is several times smaller than the opening size of the mold 5 is arranged below the servo nozzle main body 3A, and is attached to the mold 5. The mold 5 is made of copper-based metal with good thermal conductivity and is internally forcedly cooled, and is supported by vibrator/linders 6 on both sides. Although not shown, this mold 5 is guided by a low sliding resistance guide (for example, a hydrostatic bearing guide, a linear roller bearing, etc.) so that it can vibrate in the slab drawing direction. The vibration cylinder 6 is equipped with an electro-hydraulic servo knob, and a desired waveform (for example, a sine wave, a triangular wave, etc.) is input from the micro-vibration command unit 15, and the synchronous control circuit 14 outputs both left and right vibrations. The vibration cylinder 6 causes synchronous vibration.

Note that 8 is a balance cylinder, and the hydraulic pressure is set by an electro-hydraulic servo pulp in order to balance the vibrating weight mainly of the mold 5 by using the lower part of the vibrating cylinder 60.

Further, 10 is a belt constituting a synchronous mold and is guided by belt guide rollers 11. 12 is a cooling pad, and 13 is a cooling spray nozzle.

According to such a configuration, the molten steel 16 starts to solidify from the upper end of the mold 5, and the solidified shell 17 grows, but in the case of high-speed casting, the mold length LM cannot be increased as described above. For example, if the mold length Lx ==600W+ and the casting speed V=15m/m, the solidified thickness D at the exit side of the mold
is D=K F9=21βI sword, 5=4.2am.

Here, since it has not solidified even at a casting thickness of H=30 m, it is cooled further downstream by a belt synchronous casting/single support device. The support direction of the belt 10 is changed by a belt guide roller 11, and a cooling pad 12 performs direct cooling of the belt and indirect cooling of the slab. Also, since the cooling hood 2 has the role of suppressing the balance of the slab due to the static pressure of the molten steel, the spacing is set in accordance with the thickness H of the slab. By doing so, high-speed casting of thin-walled slabs can be realized.

Note that the entire device has the arrangement shown in FIG. 5, for example. That is, pouring hot water from the ladle 18 into the tundish 1,
After cooling, the molten metal is poured into a mold 5 equipped with a servo nozzle 3, cooled and milled using a belt guide 19 in which the slate is drawn out in a curved manner, and after complete solidification, it is bent again using a straightening roller 22. It is then supplied to the next process. This arrangement has the advantage that the height of the equipment is low.

Note that this arrangement is not limited to that shown in FIG.
As shown in the figure, it may be vertical until the solidification is completed, and then it may be bent. That is, the vertical belt guide 20 is placed 1 tll below the mold 50, and after solidification is completed,
The slab is bent by a bending roller 21, bent again by a straightening roller 22, and then supplied to the next process as a thin slab. According to such a configuration, since the mold is vertical until solidification is completed, inclusions in the molten steel are floated, so that it is suitable for continuous casting of high-quality steel that requires high internal quality.

According to such a thin wall continuous casting apparatus, as shown in Fig. 7, the production amount is 250 tons/Hr The smaller the slab thickness H, the shorter the mold length is needed to obtain
It is possible to significantly reduce equipment costs.

The table below shows the characteristics shown in FIG. 7 above.

Here, V=Q/H-B -r -60 [Effects of the Invention] As described above, according to the present invention, since micro-vibration casting is performed, onration marks can be made finer, and the servo nozzle can be fully opened. The subsurface coagulation method prevents the occurrence of wrinkles. Furthermore, in combination with a synchronous belt type mold, not only high-speed casting is possible, but also thin-walled slabs can be cast. It is possible to prevent shell breakage accidents and achieve the intended purpose.

[Brief explanation of drawings]

Figures 1 and 2 are detailed explanations of the present invention, with Figure 1 being a characteristic diagram showing the permissible length of the vibrating mold, Figure 2 being a characteristic diagram showing the temperature rise state of the belt, and Figure 2 being a characteristic diagram showing the permissible length of the vibrating mold. 3 to 5 show an embodiment of the present invention, and FIG. 3 is a side view of the main part;
Figure 4 is a front view, Figure 5 is a schematic diagram showing the overall arrangement,
FIG. C is a schematic diagram showing a modification of the overall arrangement, and FIG. 7 is a characteristic diagram showing the relationship between slab thickness and completely solidified length. 1... tanditshu, 2... immersion nozzle, 3...
・Servo nozzle body, 4... Nozzle, 5... Slight vibration mold, 6... Vibration cylinder, 7... Electro-hydraulic servo pulp, 8... Balance cylinder, 9... Slab , 10... Heald, 11... Belt guide roller, 1.2... Cooling pad, 13... Spray nozzle, 14... Synchronous circuit, 15... Slight vibration command unit, 16
...molten steel, 17...solidified shell, 18...shi-dol,
19... Curved belt guide, 20... Vertical belt guide, 21... Bending roller, 22... Straightening roller. Agent Patent Attorney Tatsunoue Unuma Figure 5 Kan 6

Claims (1)

[Claims] 1. Equipped with a vibrating mold that vibrates in the slab drawing direction, and a belt-type mold that is installed continuously on the downstream side of this vibrating mold and moves in synchronization with the slab, and injects molten metal from a tundish into the vibrating mold to form a slab. In a continuous thin-walled slab casting apparatus that continuously shapes a thin slab, the vibrating mold vibrates slightly during high cycles, and a servo nozzle is arranged between the vibrating mold and the tundish to maintain a constant molten metal level. A continuous thin-walled slab casting device characterized by: