gnitseretni - 5-8-2007 at 13:16
I have tried several times now to make cast aluminum pots but I failed every time.
What I do is I make a hole in the ground and place a 6" plastic pipe in it. I then put my sand mixed with bentonite around and in it and pack it in
there. I keep the sand on the inside of the pipe a little lower than the sand on the outside of the pipe because that will be my bottom.(I make the
pot upside down). I then take the pipe out and start melting aluminum. After I poured the molten aluminum in the cavity, on every occasion it always
bubbles, sometimes alot sometimes a little. The walls are fine but the in and outside of the bottom always ends up looking like the surface of the
moon with a hole here and there!
What can I try to get a smooth bottom?
Xenoid - 5-8-2007 at 15:03
Hi, interesting!
I guess there is moisture coming out of the sand mold.
But dry sand won't form a mold - catch 22!
Can you use a dried clay mold, it might be more stable.
Xenoid
[Edited on 5-8-2007 by Xenoid]
Mr. Wizard - 5-8-2007 at 15:33
Instead of making the mold as a hole in the ground try making it in a metal bucket or a five gallon can without a top. Try baking the mold in the can
in an oven to remove the water so you don't get steam bubbles when you pour. It sounds like you are trying to do this low budget, so I won't mention
casting plaster or CO2 treated water-glass sand molds. I haven't tried this myself, but I heard from a friend that some artisans down in Mexico used
to cast silver jewelry in molds made from dry Portland cement dampened with used motor oil and rammed into a mold. The surface was very smooth. I
can't vouch for this but it sounds like it would work.
gnitseretni - 5-8-2007 at 16:49
Using metal molds would eliminate steam problems.(and damaged sand molds from pulling out the pipe :mad
Maybe I could find two metal pipes with a 1/4" diameter difference and weld bottoms onto them to make metal pots. Then
place the smaller one inside the larger one and secure it somehow to keep it from moving and then simply fill the cavity with aluminum. Yeah damnit,
why didn't I think of that before?? That oughta work nicely! 
12AX7 - 5-8-2007 at 22:48
You need to use that sand and bentonite stuff, which is actually called green molding sand, and make a mold all the way around, top, bottom, sides,
complete. If you still get gas pockets, or you have trouble drawing the pattern from the mold, add more sand and let the water evaporate and try
again. You do need to mull the sand around after changing clay or sand content, since it works by having sand grains covered in sticky clay.
See www.abymc.com and www.backyardmetalcasting.com for more.
Tim
IrC - 6-8-2007 at 15:58
I had some Al fun one day. I dissolved Indium into Gallium, then dissolved that into around 90 percent Al (using mol amounts to arrive at
percentages). Kept the metal molten for a good while while extremely hot. After cooling, I wanted to see the shiny surface so I wiped it off with a
damp paper towel. Instant finger burn and smoke coming off! Hotter than hell! So I put a piece in water and watched it smoke and bubble until allmost
all gone. What was left was a room temp liquid mixture of the Ga-In metals as a bright mercury looking glob under the water. My guess is the Al was
going through a complex oxide to hydroxide set of reactions. Bottom line is this alloy is really cool. Not only that, but the alloy of Indium and
Gallium left over was amazingly clean and pure, whereas melting those two together alone usually gives you some oxide impurities floating around on
top the metals. The moral of the story is Al just acts funny when being melted so expect difficulties.
Forgot to mention but you all probably knew this, the bubbles coming off were H2 gas.
[Edited on 8-6-2007 by IrC]
Lambda - 6-8-2007 at 17:48
Welcome Conrad @IrC, I missed you Man !!!
No activity traces were to be found of you on the Internet, all seem to have evaporated for a long time, which worried me if all was still OK. Nice to
see you back again !!!
@gnitseretni,
Here are a few good Books on Aluminum Casting which can be downloaded via @Madhatters FTP services in the Folder.
UPLOAD / NBK2000 /
Home Foundry Casting Aluminum.pdf (1.3MB)
UPLOAD / Lambda / Molding /
Foundry Practice - A Treatise on Molding and Casting in Their Various Details (1904).rar (21.9MB)
Foundry Practice - A Treatise on Molding and Casting in Their Various Details (1909).rar (21.3MB)
Foundry Practice - A Treatise on Molding and Casting in Their Various Details (1906).rar (14.8MB)
UPLOAD / Lambda / Casting /
Magnesium Casting Technology - By A.W. Brace & F.A. Allen (Reinhold Publishing Corporation - 1957) 183s.pdf (18.9MB)
Magnesium Casting Technology - By A.W. Brace & F.A. Allen (Reinhold Publishing Corporation - 1957) 183s.djvu (16.MB)
DIY Foundry - Metal Casting Made Easy - 3 Volumes.pdf (4.3MB)
Handbook of Lost Wax or Investment Casting - By James E. Sopcak (Gem Guides Book Company - 1986) 35s(d).pdf (11MB)
UPLOAD / Lambda / Gunsmithing / Gunsmithing - By Harold Hoffman /
Casting Metal Parts - By Harold Hoffman (Action Book Publishers - 2002) 86s.pdf (3.3MB)
UPLOAD / Lambda / Furnace - Building a Gas-Fired Crucible Furnace (Gingery) /
Building a Gas-Fired Crucible Furnace - Revised 2nd Edition - By David J. Gingery (David J. Gingery Publishing - 2000) 59s(d).pdf (4.8MB)
UPLOAD / Lambda / Furnace - Electric Radiant Shop Furance /
An Improved Electric Radiant Shop Furnace - 1st Edition - By Dan Hartman (www.dansworkshop.com - 2002) 52s.pdf (6.9MB)
Enjoy !!
Lambda.
[Edited on 7-8-2007 by Lambda]
IrC - 6-8-2007 at 17:56
Thanks, I made the stupid mistake of relocating to the painted desert because the money was good without knowing there would be zero to no internet
access. Losing this connection in an hour, girlfriend is coming by to pick up her notebook with cellular modem. Actually am working on moving to
better area as far as internet acess is, but likely less money. After 10 months stranded on a desert island I realize I would rather live on less
money so I can have the web back!
Hope it will not take another 10 months for you all to hear from me again!