Rotary gas dispersion device for treating a liquid metal bath

Abstract

Rotary injector for injecting gas into a liquid metal includes a drive shaft, stirring means, means for circulating the gas and means for emitting the gas. The emitting means is entirely or partially made of at least one material capable of being wetted by the liquid metal.

Description

[0001] The present invention relates to a rotary gas dispersion device for treating a liquid metal bath, in particular aluminium, an aluminium alloy, magnesium or a magnesium alloy. The invention relates more specifically to a rotary injector ("rotor") designed to inject or disperse at least one treatment gas into a metal in the liquid state.PRIOR ART[0002] Liquid aluminium coming from electrolysis cells or remelting furnaces contains dissolved or suspended impurities. The most significant of these impurities are hydrogen, alkaline elements such as sodium or calcium and oxides, especially oxides resulting from the oxidation of the metal in the process of being treated.[0003] In order to eliminate these impurities harmful to the subsequent properties of the semi-finished product, the liquid aluminium is subjected to various treatments for the elimination of impurities. The most widely used of these treatments, which uses a combination of chemical reactions and flotation phenomena, co...

AI Technical Summary

Problems solved by technology

The search for the greatest treatment efficiency by means of an intense agitation of the bath, resulting in a permanent surface agitation often called "surface waves", which may cause the bath to spatter due to the surfacing of large bubbles and to a vortex phenomenon around the drive shaft, runs the risk of causing a "regassing" of the metal and degradation of the inclusion quality by forming surface oxides and / or by carrying inclusions or oxides from the free surface towards the interior of the liquid metal.

Such speeds bring about a large amount of wear on the moving parts of the gas dispersion device.

In addition, known rotary injectors do not enable the flow rate and size of the gas bubbles emitted to be controlled satisfactorily.

Rotary injectors comprise emitting orifices subject to risks involving blockage of the orifices and changes in the size of the orifices and blades due to erosion, which alters the quality of the gas dispersion.

In the case where the rotary injectors comprise a porous material for dispersing the gas, the pores are often too large.

Consequently, on the one hand, the bubbles are too large, lack efficiency, because the gas is insufficiently dispersed within the liquid metal, and cause harmful surface turbulence; on the other hand, it is necessary that the flow of the gas into the pores not be stopped, in order to prevent the liquid metal from penetrating therein, in particular during the non-operating periods between two castings.

Conversely, when the pores are too small, the bubbles spread out and remain large and it is difficult to introduce a high flow rate into the liquid metal.

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