Recycling aluminium

I have been using stainless steel containers as crucibles for a long time without any problems due to perforation. I always heat a new container in the furnace for several minutes to build up a oxide layer before using it to melt metal. I believe this oxide layer protects the metal from dissolving in the aluminium. I am careful not to scratch the sides of the vessel when stirring the molten aluminium.

At the end of each casting session I clean the crucible using hot caustic soda solution. This dissolves any aluminium stuck to the crucible. Once clean the crucible is inspected for any damage to the oxide layer. If there is damage to the oxide coating then I would discard the crucible.

Some of my stainless steel crucibles have been used for 30 melting sessions.

Clay/graphite crucibles also have a finite lifetime and if they fail in use this is most likely to be due to cracking. I think that this type of failure is potentially more dangerous than a small pinhole developing in a stainless steel crucible.

Mike

Mike Cox is hiding his light under a bushel - it's worth finding his artilces in MEW near the end of last year on aluminium smelting. they certainly make me want to have a go at it.

Neil

Went and had a look at my copy of "The Backyard Foundry" by B terry Aspin, (Chuck), a book well worth having, thought the bit about cans in paper bags was in there, but no, must have been in ME. The idea is that you get the cans into the melt without them being exposed to too much air, or they will oxidise almost instantly, like the pie dish mentioned a few posts ago. Ian S C

Michael,

I  also have been making castings for many years, and I just have to disagree with you, if only for safeties sake - Many sites dealing with aluminium mention the risk of using steel containers - the failures I have had were not  'pinholes' - large areas of the steel disappeared with no warning - cleaning/heating them does no good. On the other hand, crucibles can usually be seen to be cracking, and therefor avoided. As I noted, I use a thick steel can with a clay liner - so far that has survived for about three years - no cracks, no failures, no risks.

 Of course, you are free to take the risk - but at least others should be aware of the risk of getting molten aluminium at 700 degrees on their feet.

This thread has covered most of this stuff before, including comments from current contributors.

http://www.model-engineer.co.uk/forums/postings.asp?th=45889

Edited By wotsit on 24/02/2012 10:33:31