JPH036318A - Method and device for cleaning molten metal - Google Patents

Abstract

PURPOSE:To improve the effect of accelerating the rise of bubbles by ultrasonic waves by specifying the method for impressing the ultrasonic waves in the method for rapidly reducing the pressure of a molten metal in which a soluble gas is dissolved and impressing the ultrasonic waves on the molten metal during the generation of the fine bubbles. CONSTITUTION:The molten steel 3 is put into a vacuum vessel 1 which is, for example, a rectangular parallelepiped, and the vessel 1 is kept at a prescribed temp. and vacuum degree in VAD equipment. Gaseous N2 is then bubbled from the bottom of the vessel. The pressure is thereafter rapidly reduced to the prescribed vacuum degree and is rested. Ultrasonic generators 2a, 2b adjusted to resonate by parting the same at a prescribed distance are provided on the opposite surfaces 1a, 1b of this vessel 1. The ultrasonic wares of the same phase are generated from these two points and are impressed on the molten steel 3. The crossinterference of the ultrasonic waves is prevented and the aggregation and integration of the gaseous bubbles are additionally accelerated by this method. Since the floating rate of the bubbles is additionally increased, the time for the cleaning treatment of the molten metal is shortened.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a molten metal cleaning method and apparatus for removing inclusions from molten metal. [Prior Art] The present inventors have proposed the following in order to improve the efficiency of removing inclusions from molten metal. That is, a gas soluble in the molten metal is dissolved by bubbling, and fine gas bubbles are generated in the molten metal by reducing the pressure. According to this method, even minute inclusions in the molten metal are trapped by the bubbles and floated to the surface, resulting in extremely high inclusion removal ability. Furthermore, in order to shorten the time required for the above treatment, the present inventors have devised a new configuration in which ultrasonic waves are applied to the molten metal while the fine gas bubbles are being generated. This method applies the characteristic of ultrasonic waves that when ultrasonic waves are applied to dispersed fine particles under certain conditions, they aggregate and coalesce, to the method for cleaning molten metal described above. Since gas bubbles are thought to be generated with fine inclusions in molten metal as nuclei, by applying the ultrasonic waves, fine gas bubbles can be aggregated and coalesced together with the inclusions.
As a result, bubbles with larger diameters are generated and the floating speed of the gas bubbles is increased, making it possible to shorten the processing time. [Problems to be solved by the invention] The above-mentioned technique of applying ultrasonic waves is an excellent method for shortening the processing time, but when the amount of processing times is large, It still takes time for the gas bubbles to rise, and the above-mentioned effects of ultrasonic waves are not fully exhibited. The present invention was devised in view of the above-mentioned problems, and it is an object of the present invention to provide a method and an apparatus for making the effect of the above-mentioned ultrasonic wave application technique even more effective. [Means for Solving the Problems] Therefore, in carrying out a method for applying ultrasonic waves when fine gas bubbles are generated, the present invention emits ultrasonic waves from two or more locations. However, if these ultrasonic waves have different frequencies or are out of phase, they will interfere with each other, and the above-mentioned effect of aggregation and coalescence of gas bubbles will not occur as originally expected. It became clear that the price would not rise as high as expected. Therefore, the present inventors studied the conditions under which mutual interference would be eliminated when ultrasonic waves are emitted from two or more locations, and created the following method of the present invention and a second device of the invention related to the apparatus for implementing the same. That is, in the method of the present invention, when applying ultrasonic waves to molten metal from two or more locations, three ultrasonic waves of the same phase are applied while resonating. This resonance synergistically increases the amplitude of the ultrasonic waves, further enhancing the effect of aggregation and coalescence of gas bubbles.
It is possible to further shorten the standing time. In addition, in carrying out the first invention method, it is first necessary to use a processing vessel capable of generating fine gas bubbles from molten metal by decompression processing, so that such processing can be carried out. We decided to use a vacuum container. Furthermore, when two or more ultrasonic oscillators are installed in the vacuum container, it is necessary to ensure that the ultrasonic waves emitted from them cause a resonance phenomenon. Therefore, as the resonator, oscillators that emit ultrasonic waves of the same phase are used, and the mounting positions of these oscillators are such that the frequency of the emitted ultrasonic waves is f
Hz, it shall be installed on the opposite wall of the vacuum container with the following formula: Q = n - where C: speed of sound (m/s) 4 - n: an arbitrary integer distance cL (m) . [Examples] Specific examples of the present invention will be described below. 50 tons of molten steel (3) was placed in a rectangular parallelepiped vacuum vessel (1) shown in Figure 1 and Figure 2, which shows the horizontal cross section taken along the line X-X.
and heated the container (1) at 1660°C in the VAD equipment.
While maintaining the pressure at 650 torr, 6 Nrr[' of N2 gas was bubbled from the bottom of the container for 10 minutes. Thereafter, the pressure was rapidly reduced to 1 torr and left to stand. On the opposing surfaces (la) and (lb) of this vacuum container (1),
Ultrasonic oscillators (2a) (2b) adjusted to resonate at a distance of about 0.6 m are installed, and these oscillators (2a) (2b) are connected to a synchronizer (not shown).
This allows ultrasonic waves to be generated in the same phase. The present inventors also implemented the method of the present invention in which ultrasonic waves of approximately 20 K7 were applied to the molten steel (3) from the ultrasonic oscillators (2a) (2b) one minute after the start of the decompression treatment. Furthermore, the present inventors equipped a vacuum container similar to the vacuum container (1) above with an ultrasonic oscillator, but the oscillator was poorly synchronized (Comparative Example ■), and only one ultrasonic oscillator was used. Using the equipment provided (comparative example ■), approximately the same N2 as above
An experiment was also conducted in which gas dissolution treatment and depressurization treatment were performed, and ultrasonic waves were applied to the molten steel (3) from 1 minute after the start of depressurization. Figure 3 shows the T-contains in molten steel (3) during these treatments.

It is a graph diagram showing changes in [0]. In the figure, point A indicates the point at which depressurization was started after 10 minutes of N2 gas bubbling, and point 8 indicates the point at which ultrasonic wave application was started. As is clear from the figure, in the case of the example of the present invention, T.

The processing time after the start of pressure reduction until [0] becomes 7 ppm is shortened by about 2 to 5 minutes. This reduction in processing time is due to the resonance of the ultrasonic waves emitted from two locations, which enhances the aggregation and coalescence effect of gas bubbles that trap fine inclusions.
This seems to be due to an increase in the floating speed of the gas bubbles. [Effects of the Invention] As detailed above, according to the method of the present invention and the apparatus for implementing the same, ultrasonic waves are applied to the molten metal from two or more places at the time when fine gas bubbles are generated, and these ultrasonic waves As the gas bubbles resonate, the aggregation and coalescence of gas bubbles is further promoted, and their floating speed is further increased.As a result, the processing time required for the previously proposed molten metal cleaning method is further shortened. It becomes possible to force them.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the equipment of the second inventive device used for carrying out the method of the present invention, FIG. 2 is a horizontal cross-sectional view taken along the line X-X from the previous time, and FIG. T・ in the molten steel during the implementation of Comparative Example I・■

It is a graph diagram showing changes in [0]. In the figure, (1) shows a vacuum vessel, (la) and (lb) show opposing surfaces, (2a) and (2b) show an ultrasonic oscillator, and (3) shows molten steel. 7- -8= LL to α

Claims (2)

[Claims] (1) Dissolve soluble gas in the molten metal, then rapidly reduce the pressure to generate fine gas bubbles in the molten metal, trap inclusions floating in the molten metal, and remove them after floating. A molten metal characterized in that, in performing a molten metal cleaning method, after fine gas bubbles are generated, ultrasonic waves of the same phase are applied to the molten metal from two or more locations while resonating. cleaning method. (2) A vacuum container capable of carrying out depressurization treatment while holding the molten metal, thereby generating soluble gas from the molten metal as fine gas bubbles, and a vacuum container on the opposite wall of the container according to the following formula. A molten metal cleaning device l=n・c/f, characterized in that ultrasonic oscillators that emit ultrasonic waves of frequency f and the same phase are provided at a distance l shown in FIG. Sound wave frequency c: Sound speed n: Any integer