Specialized metallurgical processes – compositions for use therei – Processes – Process control responsive to sensed condition
Patent
1996-07-02
1999-06-01
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Process control responsive to sensed condition
75600, 75601, 266 91, 266207, 266227, 266239, 266900, 266901, C22B 2622
Patent
active
059084880
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for melting magnesium and a magnesium melting furnace with a first chamber to accommodate the melt and a device for feeding the material to be melted into the first chamber.
Magnesium is being increasingly used as a material, particularly for the manufacture of castings. Magnesium is, in a similar manner to aluminium, produced using an electrolysis process and is cast into bars, slugs or pigs which are melted in special melting furnaces before being further processed. During this process works scrap is added. The higher the share of works scrap is, the greater the contamination of the starting material being fed into the melting furnace is.
An arrangement for melting slugs and pigs and the further processing of molten magnesium is known from the DE 41 16 998 A1. Material to be melted is fed into a melting furnace via a refill orifice situated above the melt. The melt is withdrawn from the melting furnace below the surface of the melt via a siphon-like connecting line and passed into a casting furnace. The melt in the casting furnace serves as feedstock for further processing to castings. For further processing the molten magnesium is withdrawn from the casting furnace via a second siphon-like connecting line and fed into a casting die.
The disadvantage of this known plant is the high expense during commissioning owing to the use of two furnaces and the siphon-like connecting lines. The entire plant including the siphon-like connecting lines must be heated to above the melting point of magnesium so that a molten melt is present both in the casting furnace and in the melting furnace. The pressure in the casting furnace then has to be increased with a special pressure line so that the siphon-like connecting lines are completely filled with molten magnesium. Once the pressure has been reduced again, the melt levels in the two furnaces balance out so that when molten magnesium is removed from the casting furnace via the siphon-like connecting lines for further processing, magnesium from the melting furnace flows in to replace it.
The use of two separate furnaces is unfavourable as far as energy consumption is concerned and leads to relatively high construction costs.
Furthermore, such an arrangement does not permit the use of contaminated works scrap as the melt in the melting furnace must be relatively pure when it is withdrawn via the siphon-like connecting line as no further cleaning steps take place in the casting furnace.
It is the object of the present invention, to reduce energy losses during the melting of magnesium and the preparation of a purified melt whilst also reducing the construction costs.
The use of at least one second chamber makes it possible to combine the melting and purification of the melt in one melting furnace. As the melt is purified, it is possible to use a heavily contaminated starting material, for example a starting material with a higher old scrap content. Thanks to the special guidance of the flow of melt by suitable arrangement of the passage and outlet, a large part of the impurities can rise to the surface of the melt or sink to the bottom of the chambers, from where the impurities can easily be removed. Turbulences which are caused in the first chamber (melting chamber) by the immersion of the material to be melted and by the convection currents generated by the burners impair the settling or rising of impurities. This disadvantage is compensated for by the melt flowing over into the at least one second chamber (the holding chamber). No turbulences occur in this chamber; the impurities can rise or settle. The arrangement of the passage and the arrangement of the outlet are selected in such a manner that as few impurities as possible are carried through with the flow.
Thanks to the flow guidance in the multiple-chamber furnace according to the present invention sufficient purification of the melt is possible without cleaning salts being added to the melting bath. Dispensing with the addition of salt means that the environmental impact
REFERENCES:
patent: 2793852 (1957-05-01), Harrison
patent: 4385931 (1983-05-01), Wallevik et al.
patent: 5211744 (1993-05-01), Areaux et al.
Rauch Erich
Schroder Dominik
Andrews Melvyn
Rauch Fertigungstechnik Ges. m.h.H.
Schmitz + Apelt LOI Industrieofenanlagen GmbH
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