Specialized metallurgical processes – compositions for use therei – Processes – Free metal or alloy reductant contains magnesium
Patent
1991-11-01
1993-06-01
Andrews, Melvyn J.
Specialized metallurgical processes, compositions for use therei
Processes
Free metal or alloy reductant contains magnesium
266158, C22B 905
Patent
active
052155730
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of treating a metal melt in a ladle, in which a gas or gas/powder mixture is introduced to the melt in a substantially completely filled ladle and departing gas is removed by suction through a hood mounted above the ladle. The invention also relates to a ladle arrangement for use in such treatment of a metal melt.
Steel is produced from pig iron, scrap or sponge iron starting materials which are melted and decarburized in different types of furnaces, converters or like apparatus. The metal melt is handled and transported with the aid of ladles having a volumetric capacity which is adapted to the process concerned. The ladles have the form of upwardly open vessels.
Steel could be manufactured more effectively if the time that the melt spends in a ladle could be utilized to effect some part of the treatment to which the melt shall be subjected. For instance, this would decrease the time spent by the melt in a converter. In modern times, the term ladle metallurgy includes such efforts to utilize the ladle as a treatment station in steel manufacturing processes.
Examples of those processes to which the melt can be subjected in a ladle are the various purifying processes effected by introducing additives into the melt and agitating the melt with the aid of gases, and the introduction of pulverous alloying substances and slag formers, which is often effected in combination with the supply of a gas so as to achieve effective admixture of the alloying substances with the melt. Since the ladle is relatively deep, effective admixture of material with the melt with the aid of gas can be achieved when the additive material and the gas are introduced into the ladle at a location adjacent the bottom thereof.
When applying ladle metallurgy, one problem is that only a very restricted gas flow can be delivered to a full ladle, since otherwise splash-over becomes unacceptable, or the melt "boils over" the ladle rim. The volumetric capacity of the ladle is namely so adapted to the process concerned as to be substantially totally filled with melt. It is therewith impossible to reduce the volume of melt in the ladle, for practical and economic reasons.
By way of comparison, it can be mentioned that in those processes in which gas is delivered to converters, the converters are filled only with a relatively small volume of melt, therewith enabling the specific gas flow to be maintained at a very high level. It can be mentioned as an example that in the case of the process known under the acronym BOF (Basic Oxygen Furnace), the converter is normally filled with melt solely to 10% of its volumetric capacity, therewith enabling a specific gas flow of 4.0 Nm.sup.3 /ton/min to be used. When manufacturing stainless steel in accordance with the AOD-process (Argon Oxygen Decarburization), the converter is filled to 50% of its volumetric capacity, permitting a specific gas flow of 1.0 Nm.sup.3 /ton/min to be used. On the other hand, in conventional ladle metallurgy, the ladle is normally filled to about 90% of its volumetric capacity, wherein a specific gas flow of only 0.002 Nm.sup.3 /ton/min can be used. It is quite probable that this low gas flow is the reason why, for instance, the hydrogen content of the melt cannot be decreased to any appreciable extent when treating the melt with an inert gas.
Accordingly, the prime object of the present invention is to solve the problem of enabling metal melts to be treated effectively in ladles of conventional design, by delivering large specific gas flows to such ladles without the melt bubbling over or splashing from the ladle.
The inventive solution is based on the realization that the aforesaid object can be achieved by providing above the ladle a closed splash chamber of sufficient volume to permit "boiling over" and splashing to take place without detriment when introducing large quantities of gas into the melt. The splash chamber must also be so configured that molten metal which splashes from the ladle is returned effectively to the melt in said
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Patent Abstracts of Japan vol. 7, No. 147, C173 Abstract JP 58-58220 pub. 1983.
Jonsson, Lars et al "Gasteknik; Gjuterier" 1984 Eskilstuna Offset Sundbyberg.
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