Aluminum Molds

noname · Sun Sep 09, 2007 8:32 pm

Does anyone know of anything I can use for a mold, that can handle molten aluminum? I've made a couple out of plaster of paris, but I'm not sure if those will work, because I haven't tried them yet. I'm looking for something relatively cheap (like plaster of paris) because I have a limited budget.
If someone comes up with a good idea that I can use, and I actually end up using, I'll give them $5 off an aluminum vortex block. The full price for aluminum vortex blocks will be $10.

singularity · Sun Sep 09, 2007 9:11 pm

aren't a lot of metal molds made from sand? i have no clue how they make them but im sure i saw someone using a sand mold for metal casting.

FeLeX · Sun Sep 09, 2007 9:21 pm

Yea sand can be used for aluminum casting. You making a model of what you want to cast out of Styrofoam first and then you place it in the sand. As the aluminum fills in the mold it melts away Styrofoam. Look it up on youtube theres a lot of good tutorials on this.

blind909 · Sun Sep 09, 2007 9:48 pm

or just pm spuddin, he makes them

Gepard · Mon Sep 10, 2007 1:03 pm

Yeah most are sand but you do get a crap surface finish.....

Spuddin · Mon Sep 10, 2007 1:44 pm

sand is the way to go. you want to use clean sand with very little water mixed, just enough water to get the sand to cling together but be careful because you dont want alot of moister reacting with the liquid AL. the styrofoam insulation board works good for a pattern, u can get it at the lumber yard or just pull it off your house...
u can cut it easy with a bread knife but if you want a very smooth surface u need to coat the foam block with wall plaster and let it completely dry, this forms a smooth inside surface but its not needed for a vortex block.
wood patterns is also used but it requires a split sand mold which is complicated.
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Fnord · Mon Sep 10, 2007 4:54 pm

Plaster will hold up fine. Just get the mold fairly hot before you cast, otherwise it may crack. Aluminum melts at about 1200F if I remember right (It should be glowing dull red in the dark).

Spuddin · Mon Sep 10, 2007 5:40 pm

to be honest i would not use a plaster of paris mold, i've heard of it cracking even with molten lead it might last one or two castings then crack so i've heard and lead melts at around 700-800F. just too risky for something so dangerous. sand has been used for centuries and its free.

Fnord · Mon Sep 10, 2007 6:35 pm

Lead melts at ~630, assuming it is pure.

The point of heating it up first is to prevent cracking. If you heat it slowly, you can get glowing bright yellow and even cast steel if you want. It becomes powdery at around 1500F, and chunks will break off if you are rough with it.

Anyway, if it cracks, it cracks. It doesn't explode or anything (provided you made it correctly).
You should be wearing goggles and gloves anyway.

Now, here is my only problem with sand: The ways described above only uses water to hold it together. If it doesn't get damaged by the act of pouring the aluminum in, the bubbles from the boiling water will make your object unusable (unless you are making a paperweight).

Also, having moisture in contact with molten aluminum can cause it to explode and send beautiful silver streams of face-altering liquid metal in your general direction.

noname · Mon Sep 10, 2007 9:17 pm

I'll try sand if the plaster molds don't work. I've made 3 plaster ones; hopefully they aren't completely useless.

Spuddin · Tue Sep 11, 2007 9:25 am

Now, here is my only problem with sand: The ways described above only uses water to hold it together. If it doesn't get damaged by the act of pouring the aluminum in, the bubbles from the boiling water will make your object unusable (unless you are making a paperweight).

Also, having moisture in contact with molten aluminum can cause it to explode and send beautiful silver streams of face-altering liquid metal in your general direction.

you would be surprised how well it works, it takes practice and after you learn a few tricks you end up with very nice castings. when you use wall plaster to coat the foam it creates a hard shell around it and after you pour the AL the shell stays intact and leaves a very smooth surface. the bubbles does not "boil the water" it creates some steam and the foam melting away creates gas, this is why you must have "vents" for it all to escape and not distort the casting. of course not every casting comes out perfect but alot do.
you can read more about it at www.backyardmetalcasting.com

Benster · Tue Sep 18, 2007 2:15 pm

what do you use to melt the AL?

Fnord · Tue Sep 18, 2007 2:31 pm

I prefer to use a magnifing glass on a hot, sunny day.
If it's cloudy, I use my E-Z bake oven.

Benster · Tue Sep 18, 2007 2:50 pm

nice! LOL

really though, is it a technical premade smelter, or something you made yourself?

Fnord · Tue Sep 18, 2007 3:19 pm

Actually, the second line was also bs.
(Yeah, I know, that was the most helpful post in the universe)

I have a forge in my back yard which consists of nothing more than some bricks and a cooling fan.
You might be able to get a fire hot enough without a fan, since aluminum melts at a relatively low temperature. Buy a bag of charcoal and make a nice pile of it around a soup/coffee can and get it burning.

If it doesn't want to melt, use a blowdryer to get the fire burning hotter.

(you put scrap aluminum in the can, by the way, as it is made of steel).

Aluminum Molds

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