I need to make a small 3" x 1" part and want to create a mold from the
broken part I have. I'm looking at two options here.
1) Buy a large piece of aluminium and try to mill it to specs.
2) Create a mold and pour a new one.
I'm wondering if someone can tell me if the following is possible or what I
need to do.
a) Can I melt aluminium in a cast pan using a propane stove? How do I melt
b) Can I create a mold using drywall plaster? What should I use?
For this size part, this is your best option. Foundry work is quite a bit
more involved than you think. Lindsay books has a number of books on the
subject of AL foundry work. Plan on a bit of time to build up equipment and
experience before doing anything for real.
I guess for some reason I'm not giving everyone near enough credit, in my
head I pictured a couple evenings to make the mold and then another evening
to melt the aluminium and pour the mold.
Just wondering since I would love to test this anyway, if time wasn't a
problem could I use drywall plaster? or I've read about using plaster of
paris? The only problems I've read about is making sure there is enough
drytime for the mold.
No, it takes an enclosed furnace to melt aluminum. There are many good
hobby sites that will show how other people do this. Try
for starters and that site will
take to many others on hobby casting.
You should use a sand mold. Any sort of gypsum plaster has a natural
affinity for water and has to be very dry before using. Too much water
in a mold will cause a steam explosion. Again, looking at some of the
websites above will make you more familiar with sand casting.
No, and No!
Unless you have direct supervision/help/consultation from someone who has
the experience and special tools to do this don't try it yourself. The
method you are describing is 100% guaranteed to result in disaster!
in college we did lost wax casting, i think they called them "investment"
molds, built up plaster of paris & sand. we were pouring bronze. it really
would be a very involved project, would take lots of time and money and even
then there is no guarantee the casting would fit. i think there would be
considerable risk of shrinkage and warpage that in the case of sculpture may
not be a big deal but probably for a car part you may be better off *filing*
by hand it from a solid block of aluminum and expend the same amount of time
energy money to get a better result. you may have to cast a couple or a few
or maybe even several to get one you could use. that's the way i remember
it anyhow, from 1977-1982.
i just re-read your post. sorry. 3" x 1" is pretty small! almost sounds
like you could use jeweler's casting techniques. i don't know how much
metal they (jewelers) can melt at a time but i remember seeing a centrifugal
sling thing they use for jewelry to sling the molten metal into a... maybe
it was even a silicone rubber mold? maybe plaster, can't remember.. i'd
guess silver melts at a lower temperature than aluminum so i don't even know
if they'd be willing to try. maybe zinc? find out and maybe sign up at a
local college that has a continuing education jewelry class. maybe meet
some college cuties too? :-)
First, the Al you can scrounge is the wrong type to use. Cans are trash. 6061
is not for casting.
Second, you will get a certain amount of Hydrogen gas in the Al. Can you handle
tons of holes ?
(sponge? ) or use a Chlorine gas of sorts to steal the Hydrogen and make
Hydrochloric acid to boil off...
Plaster has to much water in it after it drys. It will explode nicely.
Really, if you can machine a chunk down - that is the fastest way, cleanest and
likely to make it way.
Go try it. I did, made a furnace, made molds (some sand, some plaster, some just
compressed cement powder. Nobody got hurt, it wasn't a big deal. Molten aluminum
seems to eat cast iron pots though, watch out for that. I melted brass after
that, again lots of fire and I'm intact. Plaster molds have to be really dry,
and if you dry them too fast the crack. Nobody's an instant expert, experiment.
OMFG!!!!!!!!!111111 I DI3d3d!!!!!111!!!111oneone
As you can guess from my expression, I've been doing this for years, without
direct consultation from a foundryman (ameteur or professional).
"California is the breakfast state: fruits, nuts and flakes."
"lionslair at consolidated dot net"
Pretty much, but there is still use for them, if you get them for free and
want to bother seperating the metal from the mush.
For a one-off it's not the way to go.
Odd, how have hundreds of people used it, then?
Namely zero, if you don't stir the melt.
Martin, even on my most gassed melts, I've never seen a sponge. Quite
honestly, if it were that easy to make a sponge, it would have dramatic
impact on the composite industry! Just think: stiff, lightweight 3D
aluminum honeycomb without the expensive fabrication!
If you *do* stir too much and let gas get in, an application of pool shock
(calcium hypochlorite which decomposes on heating, releasing chlorine gas)
works nicely. You need a fluxing tool to hold it at the bottom so the
bubbles pass through the metal.
Not quite, it will make a horrible mess of aluminum though, at the very
least full of holes and bubbles, and at the worst, shooting it back out of
This is remidied by heating to red heat over a few hours; the chemically
bound water is driven off and it can be poured safely.
To the OP:
If you can accept zinc or potmetal, you can get by with baking it in the
oven, 500 degrees for an hour or two. A good potmetal is as strong as
Sand molding is your best bet, but a one-off plaster and sand mold (mix 1
part plaster of paris with 2 parts sand, finer sand the better) may be best.
Mind that you need to seal it up so metal doesn't leak out! This is usually
done by melting and burning out a wax pattern, a messy job that needs a
burnout kiln to do it justice.
Oh, and as for melting aluminum, no stove will cut it. You can however melt
it in a tin can over charcoal. Burn out the tin can first, otherwise the
aluminum will eat right through it!
"California is the breakfast state: fruits, nuts and flakes."
But you have experience and you didn't try to duplicate a needed part right
off the bat without some experience. That is what I was trying to say.
Someone just doesn't decide to do this one weekend and have a perfect part
with his first attempt. And you have to have some idea of how to do it. You
don't use a pan on the stove like he was alluding to. That is just plain
stupid and dangerous. I was trying to help him understand and not to get
hurt or burn his house down.
shows how we made an aluminum part from a
broken plastic one. Aluminum melts at 1200 degrees
F and pours at about 1300 degrees so a furnace
Scrap aluminum parts that has previously been
cast can be used for your project. Aluminum extrusions,
swarf and cans should be avoided. You might also
consider zinc. It has a lower melting point under 1000
degrees. There is some info about lost foam casting
with zinc at
Drywall plaster has the potential to explode.
We use investment for lost wax casting that is
heated to 1350 degrees F and would be another
option for your part. Investment casting is indicated
if your part has undercuts.
Hope this helps
Rather than plaster, use investment. It works like plaster, but it
is intended for use at molten metal temperatures. You'll find it at
a jeweller's supply place.
It should be calcined (baked) before use.
Which drives out the moisture, so the mold doesn't create gassing problems,
or blow apart from steam pressure. Such a mold is generally poured
right out of the burnout oven, while still hot. The molds are generally
poured by the use of a centrifuge, or even with a vacuum casting unit.
Both systems are employed by jewelers.
If you are bent on doing this yourself, you will find a wealth of info
and plenty of help here:
But for one part, you may want to consider having it done for you.
There are several people on the castinghobby group that will be glad
to do it for you. You may even be lucky enough to find someone near
As to a source of zinc, outboard motors use sacrificial anodes that
are pure zinc. Most junk yards or scrap metal yards will sell the old
ones to you.
Zinc is usually alloyed with AL and Copper to make a very strong
alloy, comparable in strength to cast iron, and it still can be melted
below the melting temp of AL. You melt the zinc first, and the other
metals will dissolve in it well below their own melting temperatures.
Commercial alloys like ZA-12 or ZA-27 are made this way. The digits
signify the percentage of AL.
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