On Tue, 23 Dec 2014 15:05:12 -0500, Ed Huntress wrote:

On Tue, 23 Dec 2014 13:13:44 -0600, "Terry Coombs"
wrote:

Neon John wrote:
On Sun, 21 Dec 2014 17:43:29 -0600, "Terry Coombs"
wrote:


It's been a while since I molded and cast anything , so I decided
to get a little practice today . First melt was an old cast aluminum
decorative skeleton key . Wall hanging doodad , about 2 feet long and
4 or 5 lbs of aluminum . Next was to mold up a disc that'll be an end
cap on a ball mill cylinder . That went well so I cut up a couple of
ingots snd fired the furnace back up . I'm going to have to address
the hydrogen porosity I'm seeing with some of my stock . I've tried
chlorine pool granules and that works well enough , but the fumes
are dangerous so I'm thinking about bubbling some CO2 in the melt to
degas .

In my testing, any (relatively) inert gas will work about as well,
which is not very.

The ultimate solution is to prevent hydrogen pickup in the first
place. Induction heating with a tight fitting crucible cap pretty
much accomplishes this objective. So does purging a closed crucible
in a combustion furnace with inert gas.

If you do have hydrogen in solution, this stuff is the best I've found

http://www.budgetcastingsupply.com/p...p/2011-010.htm

It looks like charcoal and stinks badly in the can. It must be held
at the bottom of the crucible until the reaction is complete. They
sell pellet holders for large batches but for the small batches I do
(20 pounds or less), I made a plunger out of a large stainless sewing
thimble, perforated by many tiny holes and a SS rod welded to the tip.

John

I'm doing the same thing using pool chlorine granules . My cup needs
to be
larger I think . How do you load your cup ? I wrap the stuff sometimes
flux in foil and push it in . Plunge and stir and stay upwind of the
fumes .
I'm not real likely to go induction or resistance , I like the setup
I'm
using . Covering the crucible is an option , though that would make it
difficult to add stock as it melts down . I think part of my problem is
that this stuff came from stuff like truck rims and other dirty scrap .
I also have some once-melted in an electric furnace stock that doesn't
have the porosity problems .

I'm not a caster, but I've read that motor oil on dirty aluminum is a
major source of porosity problems. That source recommended soaking your
scrap in a warm lye solution to get rid of the oil.

But don't leave it in for long, because lye will also get rid of your
aluminum. d8-)

Perhaps it works because it etches off the oily layer of metal.

Dunno, just a guess...

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com