Aluminium melting slag

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Aluminium melting slag

Post  irk on Sat Jul 21, 2012 4:21 am

I have a problem of slag formation in aluminium melting process.
We remelt brikets of pressed aluminium chips in an induction furnace. After the brickets have meletd a large amount of slag forms on the molten aluminium surface. The slag is mixed with aluminium and we can not separate them.
Does anybody know how to do that?

irk

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Re: Aluminium melting slag

Post  Dmitri Kopeliovich on Sat Jul 21, 2012 4:47 am

Aluminum turnings and chips contain a large quantity of aluminum oxide in form of a film covering extensive surface of the small scrap pieces.
When the scrap (chips, turnings etc.) melts the oxide inclusions are mixed with the molten aluminum, which retains them. The alloy, which you cast, is in fact a dross.
The oxides must be separated from the melt and removed from the furnace prior to pouring operation.
Use a drossing flux (eg. Foseco's or other). Drossing fluxes react exothermically with oxides. The heat generated by the reaction promotes the coalescence of the molten aluminum drops surrounded by the oxides. The aluminum flows down and separates from the oxides.
As a result bright shiny dross (enriched with aluminum) turns into gray, powdery and dry dross. The dross is easily removed from the aluminum surface.
(Remember: drossing fluxes may contain fluorides therefore proper exhausting system is important.)

Dmitri Kopeliovich

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