Alcan International Limited

Bruno Gariepy

Ghyslain Dube

Marc Auger

Andre Gendron

Jean Pare

Marc-Andre Thibault

When molten aluminium is treated with chlorine to remove alkali and alkaline earth metals and hydrogen, there is formed a brittle oxide crust which does not protect the metal from oxidation. This problem is solved by admixing with the chlorine a minor proportion of a gaseous compound of fluorine, preferably sulphur hexafluoride, which can form alkali or alkaline earth metal fluorides in the presence of molten aluminium. The proportion of sulphur hexafluoride to chlorine gas is preferably from 0.01 to 1.0. Ingots cast using the treated metal are free of oxide patches on their surface.

Treating aluminium with chlorine

The invention provides a new stirring apparatus for stirring the liquid metal contents of a furnace, particularly the shallow furnaces used in the processing of aluminum and its alloys. The apparatus consists a reservoir separate from the furnace of relatively large horizontal cross-section and volume, into which a vaccuum draws metal from the furnace through a nozzle, the metal then being returned by gas pressure forcibly into the furnace through the nozzle in the form of a horizontally directed jet. The cycle is repeated at sufficiently close intervals to ensure that the furnace bath is quickly and effectively mixed. The nozzle directs the molten metal entering the reservoir tangentially to swirl the metal and reduce the accumulation of dross. The reservoir comprises a bottom static part including the nozzle and a readily removable top cover carrying heaters for heating the reservoir interior and the dross that deposits on the side wall to ease its removal. The cover also carries level control electrodes, an observation port, inlet ports, etc. A pressure disturbance monitor connected to the reservoir interior is used for lower level control by detecting undesired bubbling of the pressurizing gas into the metal, and can also be used to monitor the pressure reversals between vacuum and pressurization phases. The cycles of vaccuum and pressure are controlled in a manner that maximizes the quantity of metal entering the reservoir so as to obtain the maximum stirring effect.

Apparatus for stirring molten metal

Aluminium is alloyed by adding alloying ingredients to the molten metal in an intermediate treatment vessel or ladle rather than as at present in a casting furnace. If several ladles are used to supply the casting furnace, the alloying ingredients may be added to some but not all of them. A preferred order of addition of alloying ingredients is: (i) AlF.sub.3 to reduce unwanted Na, Ca and Li; (ii) one or more of Mn, Fe, Cr, Ni, Cu, Zn and Si in powder form; (iii) one or more of Zn, Cu and Si in massive form; (iv) Mg. A ladle/impeller design is described.

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Chicoutimi, Canada

Bruno Gariepy