JPH036315A - Method for cleaning molten metal - Google Patents

Abstract

PURPOSE:To increase the floating speed of bubbles and to improve treatment efficiency by applying ultrasonic waves to a molten metal after the generation of bubbles in a method for subjecting a molten metal in which soluble gas is dissolved to pressure reduction and generation fine bubbles in the molten metal. CONSTITUTION:For example, a molten steel is put into VAD equipment by 50 tons and held at 1660 deg.C and 650torr, and N2 gas of 6Nm<3> is allowed to bubble from the bottom of a ladle by means of a porous plug in 10min, followed by rapid pressure reduction down to 1torr. Subsequently, at the point of time when 2min have passed after the initiation of pressure reduction, an ultrasonic generator provided on the wall surface of the ladle radiates ultrasonic wave of 20kHz to the molten steel. By this method, the length of time necessary for the cleaning treatment of the molten steel can be shortened.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a cleaning method 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. [Problem to be solved by the invention] However, as is clear from Stokes' law, etc., it takes a very long time for microscopic gas bubbles to float, and it is impossible to increase the floating speed. The time required for the gas bubbles to float after that ultimately determines the processing capacity, and the processing efficiency remains lower than originally expected. The present invention was devised in view of the above-mentioned problems, and aims to increase the floating speed of the gas bubbles and improve the processing efficiency thereof. [Means for Solving the Problems] Therefore, in carrying out the above-described molten metal cleaning method, the present invention basically involves applying ultrasonic waves to the molten metal after the generation of fine gas bubbles. It is a feature. [Operation] It is known that when ultrasonic waves are applied to dispersed particles under certain conditions, they aggregate and coalesce. The present invention is realized by applying the characteristics of ultrasonic waves to the above-mentioned molten metal cleaning method, and since it is thought that fine gas bubbles are generated with fine inclusions in the molten metal as nuclei, the above-mentioned By applying the ultrasonic waves, these fine gas bubbles can be aggregated and coalesced together with the inclusions, and bubbles with a large diameter are generated. Therefore, it is possible to increase the floating speed of gas bubbles. [Examples] Specific examples of the present invention will be described below. 50 tons of molten steel was placed in a 50 ton V A D facility, kept at 1660°C and 650 torr, and heated with 6 Nri' of N2 from the bottom of the ladle using a porous plug for 10 minutes.
Bubbled gas. Thereafter, the pressure was rapidly reduced to 1 torr and left to stand. Furthermore, the present inventors carried out a process completely similar to the above, and two minutes after the start of depressurization, an ultrasonic oscillator installed on the wall of the ladle transmitted 20 KHz, 50' x h and 10 kHz into the molten steel.
Examples of the present invention in which ultrasonic waves of 0 KHz are emitted were also implemented. The attached drawing shows the T content in molten steel 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, ultrasonic waves were radiated from the eight points: X (20K ball), y, (5
o In the case of the present invention example of KH2) and Z (100KHz), T・

The slope of the curve showing the change in [0] becomes steeper, and T・

[0] becomes 7 ppm in 5 minutes in the case of X, 4 minutes in the case of Y, and 3 minutes in the case of 2, which is faster than in Comparative Example H. [Effects of the Invention] As detailed above, according to the method of the present invention, ultrasonic waves are applied to the molten metal at the time when fine gas bubbles are generated, and the gas bubbles are aggregated and coalesced to float. This increases the floating speed of gas bubbles, resulting in
It becomes possible to shorten the processing time of the previously proposed molten metal cleaning method.

[Brief explanation of drawings]

The drawings show T [0
] is a graph diagram showing changes in .

Claims (1)

[Claims] Dissolve a gas soluble in the molten metal, and then rapidly reduce the pressure to generate fine gas bubbles in the molten metal to trap inclusions floating in the molten metal,
A method for cleaning molten metal, which comprises applying ultrasonic waves to the molten metal after fine gas bubbles are generated in performing the method for cleaning molten metal to be removed after floating.