Gas injector

Details Gas injector Gas injector

1990-12-14

1993-03-30

Kastler, Scott

Metallurgical apparatus

Means for melting or vaporizing metal or treating liquefied...

By means introducing treating material

266265, 266270, C21C 7072

Patent

active

051981793

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to an improved gas injector for introducing gases into elevated temperature liquids, more especially--but not exclusively--molten metals.
Gases are often injected into molten metals in vessels such as ladles, for diverse purposes. For instance, a gas may be introduced into the bottom part of a vessel to clear the relatively cool bottom area of solidification products, e.g. to remove them from the vicinity of a bottom pour outlet where the vessel has such an outlet. Again, gas may be introduced for "rinsing", or to homogenise the melt thermally or compositionally, or to assist in dispersing alloying additions throughout the melt. Usually an inert gas is used. Reactive gases may be employed, e.g. reducing or oxidising gases, when the melt composition or components thereof need modifying.
Previous gas injection proposals have included the installation of a solid porous refractory plug or brick in the refractory lining of the vessel. They can be simple, but not without various operational drawbacks. Unless very porous, when they would be unduly weak, they can limit the amount of gas reaching the melt significantly. If excessively high gas pressures are used, in order to compensate for the attenuating effect of the porous refractory, problems of sealing arise. Significant and often costly loss of gas results. Substantially all refractory materials are porous to gas, owing to the minute fissures disposed randomly throughout the refractory mass. The fissures or porosities provide meandering gas flow paths throughout the refractory body. Such haphazard flow paths are not especially helpful to the metal producer. Ideally, he would wish to apply gas pressure to an outer end of the refractory injector block and to have it issue only from the opposite, melt-confronting end of the block in a well-defined stream of gas. This does not ordinarily happen due to the wandering nature of the gas flow paths. In an effort to improve the performance of such solid injector bodies, workers in the art have resorted to directional-porosity techniques. In effect, they have tried making refractory injector bodies with a plurality of straight capillary-size passages extending from the inlet to the discharge ends of the bodies. Such passages have been created by casting or pressing refractory material in a mould about tensioned plastics or metal strands which are subsequently removed by burning or by pulling them from the refractory mass.
Whilst an injector body with directional porosity provided by capillary passages is better than an ordinary porous brick or plug, its efficiency is still less than ideal. When pressurised gas is applied to an inlet end of such a body, not all the gas flow is along the passages. Some of the gas finds its way into the porous refractory mass and thus is dissipated. Again, partly because the capillary passages are in practice less than perfect, gas can dissipate laterally from them into the surrounding refractory. The pressure of gas exiting the passages into the melt may be reduced to a level whereat the gas bubbles rather than jets into the melt. When the gas issues from a passage as a bubble, melt can instantaneously intrude into the passage and block it.
A further, and very significant problem, is how to join the refractory material of the injector body to the gas supply to provide a gas-tight seal. Known injectors have employed a metal jacket as indicated above wherein the jacket is gas-tightly secured (e.g. by threaded attachment) to the gas supply and the refractory body is cemented into the metal jacket. However, the cement between the refractory body and the metal constitutes a weakness. Although the metal jacket chamber may be distanced from the interior of the molten metal vessel by the refractory body, the jacket is nevertheless subjected to extreme elevated temperatures. Differential thermal expansion of the metal jacket, the cement and the refractory body can cause the jacket to break away from the refractory thereby breaking the gas-tight seal and causing the ga

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Radex-Runschau, Heft.3, 1983, B. Grabner et al., pp. 179-209.

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