Tom
Aluminum wheels from vehicles are generally very good to use for sand
casting. Another super item is pistons. I keep any and all pistons
separate from all other aluminum pieces.......Its some great stuff/
Degassing tablets are used to degas or allow hydrogen gas that builds
up in a crucinble of molten aluminum to dissipate and escape out of
the molten metal. This hydrogen sulphide smells like rotten eggs, and
makes a casting very porous. Once you cast something and start to
mahcine it, and you start to smell what appears to resemble rotten
eggs, what your encountering is a porouos casting with hydrogen
suplhide gas entrained in it. YOu can use regular swimming pool
chlorine tablets, ground up into a poweder or buy those one dose
packets of powder used for same purpose to save on having to pulverize
it, and add it to the mix at the rate of approx 1 tablespoon of the
material to 1 quart of crucible size or roughtly 4# of alumin. Its
added shortly after the metal has melted, and its best to add it
directly in to the bottom of the melt, by way of a tube with the
powder wrapped up in a piece of aluminum foil.....Resist all
temptations to stir your melt......it induces more air which also
induces more junk you do not want.......afterall your melting
aluminum, not making soup ;-) You can but actual degassing tablets
but they are pretty pricey, and the swimming pool tablets crushed up
work just as fine.
I fyour using a steel pipe cruicble or any any items that are made of
common carbon steel or any metal its best to coat them with a
refractory wash to further reduce contamination. You can use slip for
this coating if no actual refractory wash is available. Just thin it
out and apply it with a brush, allow to dry naaturally or place near
or over exhaust of furnace to accelerate its drying. It will harden up
and make a coatiing to keep contact of steel or metal from molten alum
to a minimum. It usually needs to be replaced after each melt or so,
so its not considered a permanent method, but in a back yard foundry
every little bit helps.
On 23 Nov 2005 14:21:48 -0800, "Tom" wrote:
===Thanks for the replies... some more questions:
===
=== Your cheapest bet for good casting material is to use sand-cast
=== aluminum scrap such as cylinder heads, transmission housings,
=== differential housings, etc. of OLDER cars where these were indeed
=== sand-cast.
===
===What's a good source for this kind of Al? A neighboring garage
===is willing to let me take the occasional Al wheel, are those any
===good?
===
===What are degassing tablets?
===
===Thanks Roy for the info, nice site too! The shaper's very
===impressive. What kind of lathe and milling machine do you
===have?
===
===Mike, if you're near Boston we can have a casting party
===to get you started with casting while you build the foundry...
===I won't do your pattern and sandwork, but will gladly pour. :-)
===
===Tom.
===http://www.TomEberhard.com
================================================== =
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