JPH04200848A - Method for preventing nozzle clogging in immersion nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To reduce the adhesion of inclusions to the inside of an immersion nozzle and to prevent the clogging of the nozzle by moving a molten metal level in an immersion nozzle up and down by periodically feeding and recovering gas into and from the nozzle. CONSTITUTION:Gas is periodically fed and recovered into and from an immersion nozzle 1, by which the inside of the nozzle 1 is pressurized and evacuated and a molten metal level in the nozzle 1 is moved up and down. By this method, casting can be done continuously for a long time because the adhesion of inclusions to the inside of the nozzle is reduced. Further, the occurrence of defects due to blow holes in a cast billet can be remarkably reduced.

Description

[Detailed Description of the Invention] <Industrial Publication Part>f> The present invention provides 3 items! 1111 L, Continuous casting #/j surface and 31 growth of inclusions on the nozzle inner wall 1m Prevent defects from occurring/i
Method C: 1 and 4, which also prevents clogging in the nozzle.

<Conventional technology> JIJ! In continuous casting, metal inclusions in 7H steel, some of which float in the tundish, but most of them separate (: [tandish j, and immersion nozzle to control the flow rate of molten steel in the mold Bring it inside J
:Reru. These jlK metal inclusions accumulate on the inner wall surface of the immersion nozzle along with the X-ray passage between the castings 11i'1 (accumulating), causing so-called nozzle clogging and inhibiting 414 productivity.

In the past, many studies have been conducted on methods to prevent nozzle clogging;
Eight shots have been advanced, but the most - boat fishing t = 'it'
Methods 1-2 and 1-2 are methods in which a liquid gas is blown into the immersion nozzle, which is effective in preventing nozzle clogging (within 11 minutes). However, inert gas injection is effective in preventing nozzle clogging, but the blown gas becomes bubbles in the molten steel and is carried into the mold 1' and into the solidified layer inside the mold.・It is blown and remains in the casting J1. These remaining W/bubbles 4; l: p) H rolling)
Even cold rI rolling can cause serious defects in crimped and scratched products. [Nozzle 4 that does not blow gas
There was a desire to establish a technology to prevent layer damage.

No. 1 in the passage of the cold 114 inside the immersion nozzle
The phenomenon of accumulation of metal inclusions ('J-11) is remarkable in areas where the flow velocity is slow in the passage, as described in, for example, Japanese Patent Laid-Open No. 63-60.
This is described in JP-A No. 055, Japanese Unexamined Patent Publication No. 2-121756, and the like. That is, '1yDn 1986-(io05
In JP-A-2-121756, the flow path at the lower end of the nozzle immersed in the molten metal is shaped so that it widens toward the lower end, thereby reducing the deceleration range of the molten steel.
In the publication, a porous body is placed in a device that corresponds to the deceleration region of molten steel in the nozzle, and the deceleration region is reduced by gas IW agitation to prevent non-metallic inclusions from accumulating on the nozzle inner wall.
We are working hard to prevent nozzle clogging. However, in any case, the inactivation into the nozzle)1-
Due to the blowing of gas, trapping of air bubbles in the slab is unavoidable.

<Problems to be Solved by the Invention> An object of the present invention is to overcome these problems and to propose a nozzle clogging prevention method that prevents inclusions 411 from adhering to the inner wall of a submerged nozzle.

<Means for solving the problem> That is, the present invention provides a continuous casting method in which molten metal in a tundish is injected into a mold via an immersion nozzle.
This is a method for preventing nozzle clogging of a continuous casting submerged nozzle, which is characterized by periodically supplying and recovering gas into the submerged nozzle to increase and reduce the pressure inside the nozzle, thereby raising and lowering the level of the molten metal inside the nozzle.

<Operation> The feature of the present invention is that by supplying and recovering a controlled amount of gas into the immersion nozzle, the pressure is periodically reduced and increased within the nozzle, and the level of the molten steel in the nozzle is adjusted in the vertical direction. By applying vibration to the nozzle, the molten steel flow in the nozzle is changed and the deceleration range is reduced.

-C, the molten steel in the immersed nozzle is freely falling onto the scene inside the immersed nozzle. That is, the molten steel flow in the nozzle is divided into a free-falling part and a part filled with molten steel that flows in a circular pipe. In such a case, the molten steel flow velocity V at the molten metal surface in the immersion nozzle is the initial flow velocity V. and falling distance (L-
r'in/ρ) as shown in the following equation. However, here, 17 is the distance from the lower end of the tandem nozzle to the molten metal surface in the mold, ρ is the molten steel density, and g is the gravitational acceleration.

That is, it can be seen that ■ changes based on changes in the nozzle internal pressure Pin. In addition, the present inventors have discovered that the nozzle internal pressure P
It was confirmed in a water model experiment that the flow in the immersed circular pipe changes as the in is changed periodically, especially the flow in the part close to the wall surface.

According to the present invention, the region in which the flow velocity of molten steel in the submerged nozzle filled with molten steel is reduced is reduced by changing the thickness of the boundary layer near the inner wall of the nozzle, where the flow velocity is reduced due to the influence of the viscosity of the fluid. . Furthermore, when pressurizing the inside of the nozzle, the height of the molten metal inside the nozzle decreases, so the volume of the boundary layer of the molten steel flow inside the nozzle decreases, reducing the amount of molten steel passing through this boundary layer and reducing the adhesion of inclusions. be done. Above 4
Due to the H-th power effect, the adhesion of inclusions to the inner wall surface of the nozzle is reduced, and clogging of the immersion nozzle can be prevented.

The waving phenomenon on the surface of the molten steel in the mold due to repeated vertical movements of the molten steel surface in the immersion nozzle hardly stops because the amount of molten steel in the mold is larger than the amount of molten steel in the nozzle.

Furthermore, in the present invention, gas is supplied and recovered into the submerged nozzle in order to adjust the nozzle internal pressure, but the supply and recovery are instantaneous, and the amount of gas supplied is extremely large compared to conventional methods. Since the amount of gas involved is small, there is almost no deterioration of the slab material due to gas entrainment.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of a pouring device used in the present invention. In the figure, reference numeral 1 denotes an immersion nozzle for injecting the molten steel 3 in the tundish 2 into the mold 4. A pressure regulating pipe 5 is attached to the body of the nozzle, and a solenoid valve 6 is used to periodically repeat pressurization and depressurization in the nozzle internal space. In addition, the vertical stroke of the scene level is controlled so that the molten steel does not reach the pressurization pipe during depressurization, and so that it does not reach the lower end of the two discharge lowers (hole diameter 8oφ) of the immersion nozzle 1 during pressurization. No yo? ε(
(It is a tonley for measuring the pressure inside the J nozzle, and 1) is an adjustment/decreasing pressure control i[+n device (Ai).

〈'): Layer side〉 1st [i<1(,i-shown/1'1 Using nostle, cast 2 low carbon Al 1 button 1 i% speed 19 1.0+it
7'min T combined R1500t
Collect the 2-spring nozzle and use Al! ] As a result of the inspection, it was found that almost all inclusions were found in the solidified casting.There were no air bubbles in the solidified casting. The occurrence rate of serious defects has been drastically reduced by 1 to 4.In addition, it was actually tested between 1+ and pressurized 3V/iJ blue for 110 seconds. ) Jjl I
During JE (It supply-), the amount of rugone gas is determined by the nozzle internal pressure (
Gauge pressure) was measured 2, -1. oomm becomes 1120 %': Yes. The pressure inside the nozzle during depressurization should be maintained at 1120mm and 1800mm.
Ru.

In the comparative example shown in FIG. 2, argon gas 'E 4 f! /m1n This shows a case where the liquid is unilaterally sucked into the nozzle.

<Results of the invention> As described in detail below, the present invention eliminates inclusions (= J) in the immersion nozzle due to loss of long-term contact &h.
The casting process becomes liJ, and the occurrence of defects due to air bubbles in the cast 11f is increased by 1.
'', the decrease was achieved by 7 months in January.

[Brief explanation of the drawing]

Figure 1 is a cross section LA1 showing an embodiment of the apparatus used in the present invention. Figure 2 is the present invention and the conventional method. , m, J, is a graph comparing the rate of occurrence of 17 defects caused by air bubbles in cast products. ■･･･････････････････････････････････････････････････････････. 4 ・
・Mold, 5. Pressure adjustment pipe, 6. Solenoid valve, 7. Nozzle discharge hole, 8. Nozzle internal pressure measurement sensor, 9. Oxidation pressure control device.

Claims (1)

[Claims] In a continuous casting method in which molten metal in a tundish is injected into a mold through an immersion nozzle, the inside of the nozzle is pressurized and recovered by periodically supplying and recovering gas into the immersion nozzle.
A method for preventing nozzle clogging of an immersion nozzle for continuous casting, which is characterized by reducing the pressure and raising and lowering the level of the molten metal inside the nozzle.