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[DPRG] Making Metal

Subject: [DPRG] Making Metal
From: Patrick Innes kc5ugq at yahoo.com
Date: Wed Oct 18 09:33:42 CDT 2000

> As I type this, my first ever (Aluminum) ingot is
> cooling down!
[ snip! ]


I've got a friend out here in semi-rural Maryland who
has a coal-fired forge out in his backyard, and just
about every weekend lately, we've been out there
pounding hot steel into submission.  

I'm also in the SCA (Society for Creative
Anachronism), where I picked up the hobby of
pewtercasting, and discovered that it can be done
easily and (most importantly) safely within the
confines of my 3rd floor apartment, no problem.

Working with heat and metal really is satisfying,
isn't it?

[ snip! ]
> As I started to pour into my mold, I finally
> understood what "dross"
> was all about.  Probably 3/4 by volume of what I got
> out of my 
> crucible appeared to be junk floating on top of a
> little pool of
> shiny liquid aluminum.  

This is one of the "joys" of working with Aluminum. 
It oxidizes before it melts, and aluminum oxide has a
higher melting point than the actual aluminum itself. 
This is why you can't (easily) cut aluminum sheet with
an oxy-acetylene torch; it forms a "shell" that you
can't actually cut through with the torch tip.  (This
>from limited experience working with aluminum -- YMMV)

When they melt aluminum commercially, they use an
inert atmosphere (Argon, maybe?), to prevent the dross
(slag, floaties, etc.) from forming.  I imagine that
you might be able to rig some sort of argon feeder
system, to deliver a steady stream of the gas into the
top of your crucible, in order to exclude oxygen, and
increase your output of useable metal.

Frederick, MD is right next to EastAlCo, one of the
larger (I think) aluminum companies around.  I could
probably find someone who works with the production
aspect of the plant, and see if they have any advice.

[ snip! ]
> then I noticed
> that the bottom of my poor dog food can had
> partially burned through.

You should be able to find ceramic
crucibles...er...somewhere.  I'm not exactly sure
where, but my friend with the forge also does jewelry
work, and has quite a few lying around.  I could ask
him where he gets his, if you would like...

A couple of books you might find useful:

"Practical Casting -- A studio reference"
by Tim McCreight  
ISBN: 0-9615984-5-X
LC #: 85-073045
This is an excellent book on casting, covering
everything from basics, to more advanced topics,
including foundry casting.  This is written more for
the jewelry-casting crowd, who will be doing a lot of
investment (lost-wax) casting, but it has plenty of
information on other forms, including RTV, sand, and
improvised-mold casting.  DEFINITELY a book to at
least check out, but if you're going to be casting,
buy a copy of this book!

"How to Cast Small Metal and Rubber Parts - second
by: William A. Cannon
ISBN: 0-8306-0414-6 
This book is written by and for those interested in
restoring automobiles and equipment with
hard-to-replace cast metal or rubber parts.  Most of
the book is about sand-casting replacement parts from
bronze, using home-made implements.  Just the thing
for the amateur roboticist!  There are chapters
detailing the manufacture of equipment, including a
do-it-yourself furnace, complete with
vacuum-cleaner-blower forced air heating.  Chapters
include multi-part molds, and how to deal with "wierd"
shaped parts.  The latter half of the book talks about
casting rubber parts from liquid urethane and other
compounds.  Amazon shows a 1-2 week delivery time on
this one, but it's available from Micro-Mark
(www.micromark.com) for $14.95 -- catalog #: 80318

Hope this helps!

(I also have some experience casting parts from white
metals -- low temperature alloys that melt around 500
degrees.  If anyone has questions about that, I'd be
glad to share what I've learned...)

-- Patrick

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