Aluminum Mold?

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 it?
b) Can I create a mold using drywall plaster? What should I use?
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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.
Karl
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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.
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wrote:

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.
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evening
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.
Harold
Harold

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HotRod wrote:

No, it takes an enclosed furnace to melt aluminum. There are many good hobby sites that will show how other people do this. Try http://www.backyardmetalcasting.com/ 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.
Gary Brady Austin, TX
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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!
Lane
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Lane <lane (no spam) at copperaccents dot com> wrote:

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.
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"Lane" <lane (no spam) at copperaccents dot com> wrote in message

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).
Tim
-- "California is the breakfast state: fruits, nuts and flakes." Website: http://webpages.charter.net/dawill/tmoranwms
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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.
Lane
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"Lane" <lane (no spam) at copperaccents dot com> wrote in message

Where did I get it?

No, of course...not...
Tim
-- "California is the breakfast state: fruits, nuts and flakes." Website: http://webpages.charter.net/dawill/tmoranwms
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HotRod writes:

Gypsum is a hydrated crystalline structure, and will not stand up to the heat of molten aluminum.
Use something like green sand.
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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? :-)
b.w.

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HotRod wrote:

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.
Martin
--
Martin Eastburn
@ home at Lion's Lair with our computer lionslair at consolidated dot net
  Click to see the full signature.
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"lionslair at consolidated dot net" <"lionslair at consolidated dot net"> wrote in message

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 the mold.
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 steel. 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!
Tim
-- "California is the breakfast state: fruits, nuts and flakes." Website: http://webpages.charter.net/dawill/tmoranwms
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Hi HotRod
Take a look at http://www.granthams.com/Repair / that 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 is required.
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 http://www.granthams.com/Casting /
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
Rod Grantham http://www.granthams.com/Projects /
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Any readily available sources for zinc?
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Post-1982 USA pennies will do in a pinch.
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The penny idea is funny. I never knew. The funny thing is that since I'm Canadian it would cost me twice as much to use US pennies :)
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If you are bent on doing this yourself, you will find a wealth of info and plenty of help here: http://groups.yahoo.com/group/castinghobby /
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 you.
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.
Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA
http://www.plansandprojects.com
The ultimate result of shielding men from the effects of folly is to fill the world with fools. --Herbert Spencer, English Philosopher (1820-1903)
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