JPH0336209A - Method and apparatus for rh vacuum degassing - Google Patents

Abstract

PURPOSE:To improve gas lifting efficiency of floating gas bubbles by increasing the circulating flow rate of a molten metal by means of improving the degassing efficiency through adding a revolving force of the molten metal ascending circulatingly in an uptake tube in a RH vacuum degassing vessel. CONSTITUTION:The gas is blown from gas blowing tuyeres 1 penetrating into iron shell 3 and a lining refractory 2 of the uptake tube 7 in the RH vacuum degassing vessel, and the molten metal 6 is ascended with the floated bubbles 5 and circulated into the vacuum vessel to execute the degassing. In the above RH vacuum degassing method, a revolving force is added to the molten metal circulatingly ascending in the uptake tube 7 to make the revolving stream 4. As the means for giving the revolving force, the above plural gas blowing tuyeres 1 are inclined toward side part to the direction toward center point 9 in the horizontal cross-sectional plane of the uptake tube 7. This inclining angle alpha is desirable to be about 5-40 deg.. Further, as the above means, an electromagnetic stirring device may be set at outer circumferential part of the uptake tube 7. By the above revolving stream 4, the bubbles 5 are restrained from being put with each other and the gas lifting efficiency can be enhanced to the max. limit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an RH vacuum degassing method and apparatus.

(Prior Art) A vacuum degassing apparatus mainly consists of a vacuum tank and a dipping tube connected to the lower part of the vacuum tank and immersed into the molten steel to be treated.

A typical example of this device is a vacuum degassing device (reflux type vacuum degassing device) in which the immersion tube is divided into an ascending tube for rising the molten steel and a descending tube for descending the molten steel. By vacuum degassing treatment, secondary refining treatment such as decarburization, deoxidation, dehydrogenation, or denitrification treatment of molten steel is performed.

In recent years, there has been a strong need to manufacture low carbon steel for cold-rolled materials and electromagnetic materials, primarily to improve productivity by significantly speeding up the annealing process. When obtaining low carbon steel, a smelting furnace (
The coal is decarburized as much as possible in a converter furnace, open hearth furnace, electric furnace, etc., and then decarburized in a vacuum degassing device to achieve a low coal value to the extent that the desired purpose can be achieved. The final carbon value obtained by this vacuum degassing apparatus is mainly determined by the rate of supply of unreacted molten steel into the vacuum chamber and the stirring state of the molten steel within the vacuum chamber.

Therefore, by increasing the supply rate of molten steel into the vacuum chamber, that is, the reflux rate of molten steel, low carbon steel can be efficiently obtained.

In order to increase the reflux rate of molten steel, it is optimal to increase the flow rate of the blown gas and improve the gas lift effect. However, as the flow rate of the blown gas increases, there comes a point where the supply rate of molten steel into the vacuum chamber does not increase but decreases, and the desired low carbon steel (for example, 20
ppm or less) could not be obtained. This is thought to be due to the so-called blow-out phenomenon in which a large amount of gas is rapidly blown into the molten steel, and these bubbles are introduced into the vacuum chamber all at once without contributing much to the lift of the molten steel. It is thought that this is because gas bubbles are more likely to coalesce because gas is blown under the same conditions by providing multiple slits with the same diameter. For this reason, in order to blow in the gas efficiently, for example, a device is installed in which gas blowing tuyeres are installed in multiple stages in the vertical direction, and the upper and lower blowing tuyere positions are shifted horizontally so that they are not on the same axis. -87447) has been proposed.

Also, in order to sufficiently stir the inside of the vacuum chamber, I? An apparatus has been proposed (Japanese Unexamined Patent Publication No. 110611/1984) in which a gas blowing tuyere is provided at the bottom of the H vacuum tank at a position between the open ends of the immersion tube tank.

(Problems to be Solved by the Invention) However, in the conventional device (Jitsuma No. M56-81441), the bubble reach distance for the gas flow rate of the plurality of gas blowing tuyere Therefore, if the blown gas flow rate is large, bubbles will be concentrated in the center of the riser pipe, and if it is small, bubbles will be concentrated near the pipe wall.
The gas lift force was efficient and did not contribute to increasing the reflux rate of molten steel.

In addition, Japanese Patent Application Laid-Open No. 57-110611 discusses the problem of corrosion of refractories near the gas injection line at the bottom of the vacuum chamber, and that when the injection gas flow rate exceeds a certain value, molten steel recirculation occurs due to the so-called air curtain phenomenon. There is a problem that the speed decreases, and furthermore, there is a problem that the splash inside the tank when the bubble bursts increases dramatically, causing problems such as an increase in metal adhesion inside the tank.

(Means for Solving the Problems) The present invention has been made to advantageously solve the problems of the prior art, and includes: (2) A RH vacuum degassing method characterized by rotating the riser pipe by giving a (3) An RH vacuum degassing device is characterized in that the RH vacuum degassing device is installed so as to be inclined to the side, respectively. R) I vacuum degassing apparatus,

(Function) When performing secondary refining of molten steel using the R11 vacuum degassing device, if a swirling force is applied to the molten steel rising in the riser pipe to swirl the molten steel flow, what happens to the gas bubbles blown into the riser pipe? 8
The gas bubbles are subjected to shearing force by the swirling flow of the steel, and the gas bubbles do not coalesce during the process of floating in the riser pipe, but reach the vacuum chamber in a dispersed state, so that the gas lift effect can be maximized.

(Embodiment) FIG. 1(A) is a longitudinal cross-sectional view of a rising pipe showing an embodiment of the present invention, and FIG. 1(0) is a view taken along the XX arrow in FIG. 1(A).

As shown in FIGS. 1(a) and 1(b), the present invention applies a swirling force to the molten steel 6 rising in the riser pipe 7 of the RH vacuum degassing tank to generate a swirling flow 4 in the molten steel 6. This is to prevent the bubbles 5 blown into the gas bubbles 5 from coalescing into a larger diameter, and to maximize the gas lift effect of the bubbles 5. As a means of applying swirling force to the molten steel 6 in the riser pipe 7, a plurality of gas injection tuyeres 1 are provided in the riser pipe 7, passing through the lining refractory 2 lined on the inner circumferential surface, at the center point of the riser pipe's horizontal section. Each gas blowing tuyere 1 is installed to be inclined laterally by an inclination angle α with respect to the direction toward
It is effective to form the swirling flow 4 by simultaneously blowing a gas such as Ar gas into the molten steel. In this case, it is desirable to set the inclination angle α within the range of 5 to 45°; if this angle is less than 5°, the effect of creating a swirling flow cannot be expected; on the other hand, if it exceeds 45°, the injected gas The gas rises in the vicinity of the refractory lining 2, resulting in the disadvantage that not only the gas lift effect is not sufficiently exerted, but also the lining refractory 2 is prevented from melting.

FIG. 2(a) is a longitudinal sectional view of a rising pipe showing another embodiment of the present invention, and FIG. 2(a) is a Y-Y line in FIG.
It is an arrow view.

As shown in FIGS. 2(A) and 2(Ill), an electromagnetic stirring device 8 is installed on the outside of the riser pipe 7 for imparting a swirling flow 4 to the molten steel 6 rising inside the riser pipe (7). By installing it, the molten steel 6 and the bubbles 5 blown into it may be swirled. In this case, a plurality of gas blowing tuyeres 1 can be installed so that each one faces the center point 9 as shown in FIG.
As shown in (b), the electromagnetic stirring devices 8
A strong swirling flow 4 can be obtained due to the mutual effect of the swirling force provided by the blowing gas flow and the swirling force imparted by the blown gas flow, and the effects of the present invention can be significantly enhanced.

Table 1 shows an embodiment of the present invention in which the molten steel rising in the riser pipe 7 was swirled using the type of apparatus of the present invention shown in FIGS. 1(A) and 1(II).

As shown in Table 1, the molten steel return flow rate when using the conventional method without providing an inclined angle to the gas injection tuyere is 07Ton/mi.
However, in the case of the present invention in which the gas injection surface was provided with an inclination angle of 30°, the molten steel return amount was 128 T/min, even though other conditions were the same as in the conventional method. Compared to the conventional method, the molten steel return amount could be increased by 16.4%.

(Effects of the Invention) As described above, the present invention swirls the molten steel rising in the riser pipe of the RH vacuum degassing device, applies shear force to the bubbles rising in the molten steel, and increases the diameter of the bubbles by coalescence of the bubbles. Since this prevents carbonization and maximizes the gas lift effect of the bubbles, it is possible to increase the reflux amount of molten steel, thus promoting the vacuum decarburization reaction and easily obtaining ultra-low carbon steel. In addition, it is expected to have effects such as facilitating degassing reactions such as deoxidation, dehydrogenation, denitrification, etc., and easily obtaining cleaner and higher purity wire.

[Brief explanation of drawings]

FIG. 1(a) is a vertical cross-sectional view of a rising pipe showing an embodiment of the present invention, and FIG. 1(0) is a view taken along the line X-X in FIG. ) is a longitudinal cross-sectional view of a rising pipe showing another embodiment of the present invention, and FIG. 2 (IJ) is a view taken along the YY arrow in FIG. 2 (A). 1: Gas injection lining, 2: Lining refractory, 3: Iron skin, 4
: swirling flow, 5: bubbles, 6: molten steel, 7: upper 0 noon, 8: electromagnetic stirring device, : center point. ■ /'~ L Yuzu 3 1

Claims (3)

[Claims] (1) An RH vacuum degassing method characterized by applying a swirling force to the molten steel rising in the riser pipe of the RH vacuum degassing tank to make it swirl. (2) A plurality of gas blowing tuyeres provided on the outer periphery of the riser pipe of the RH vacuum degassing tank are each installed so as to be inclined laterally with respect to the direction toward the center point of the horizontal cross section of the riser pipe. RH vacuum degassing equipment. (3) An RH vacuum degassing device characterized in that an electromagnetic stirring device for imparting a swirling flow is provided on the outer periphery of the riser pipe of the RH vacuum degassing tank.