Instructables

A Good Crucible

Im new to the forge community and i need some advice. I built my first forge useing the charcoal and coffie can method. i melted about 20 or more cans so far and got about 86 grams of aluminum. The crucible i used was a soup that i burned through. I done that twice. While melting I got a lot of slag. Is that normal when melting cans? I also need a good crucible. What can i use for now and where can i get a good one later. I plan to make a propane forge in the near future so a few tips here would be helpfull as well. Any and all advice would be helpfull. Thank you in advance ~Jeht Black~

Goodhart7 years ago
Here is someone's post in another forum on making a good crucible: Post on Crucible
Jeht Black (author)  Goodhart7 years ago
This is good information, thank you. What type of clay do I use when makeing a crucible?
iv heard that ceramic works well. try makeing one out of fire cement using a small contaner as a mold.
I am not positive. It would have to be something that could be fired and would not crack under high heat.
Jeht Black (author)  Goodhart7 years ago
alright. thank you for the information
comander015 years ago
Ive heard that if you use the clumping kitty litter, water, and fire cement you can easily shape a custom crucible. The kitty litter gives it form and some heat resistance, and the fire cement prevents anything from melting through.
isent kitty litter a bad idea because of the chemicals in it? might be deadly if burned. u know fumes and all.
kharaku4 years ago
 I have found good ceramic crucibles here.
jtobako7 years ago
Lots of slag is normal with cans. For a crucible, if you can't find a cast iron pot (not pan, the sides aren't tall enough for the fire to keep the center hot) you can cut the bottom off of an EMPTY compressed gas cylinder. The small medical oxygen tanks work well, and are sometimes free when they don't pass inspection-very thick and last a long time without worrying about the slow heating that ceramic crucibles need. EMPTY portable propane bottles (400-500 g?) work for longer than a tin can-just make sure they are empty before cutting into them : )
exactly that is what i am using for the time being i ran outof propane in one of my many tanks (the small ones that are thin and tall) i just made sure that the gas was completely "drained" and i cut at the seam. then i made a spout and there i had an effective crucible. the only problem is that the container is a bit thin and started to flake. and another horrible thing happened i was ussing a coffee can foundry for that run while melting zinc. an ember fell into my crucible and the zinc caught on fire. it had a nasty reaction and i had to reheat and clean it out with water which weakened it. about half a pound of zinc wasted...
Zinc melts low enough (less than 800f/just over 400c) that you shouldn't need that much of a fire, just enough to set the crucible on (not in).
Jeht Black (author)  jtobako7 years ago
now that will work and i know where i can get one....my granny thanks
Might want to ask granny where she gets hers, then ask them where the cylinders go that no longer pass inspection end up : )
John Smith7 years ago
I can't believe no one linked to bacyard metalcasting. I have this book, and have built somehting similar. For crucibles, see this. For refractory formulas, see this. If you are REALLY on a budget, try this. Hope this helps!

PS- If you have any questions, PM me. Ive made a working furnace, and have melted metal on several occasions.
John Smith u have a very good link i have thoroughly read over that website a while back and finally am about to make the waste oil burner... great website anyways the only problem with the way he makes the crucible is that if u plan to melt iron ur crucible will melt away into "nothingness" i would suggest to buy a ceramic crucible or even make one out of stoneware or porceleain clay since they have higher melting temperatures than orginary earthenware clay hope this helps
Oh, and try NOT to melt cans first, melt solid aluminum first. Then, add the cans, which you should pound into little bricks to prevent oxidation. A good source of aluminum is old ladders, and short scrap pieces. Also, try aluminum chairs. You could try asking your local machine shop to save aluminum scrap. If they say no, tell them you melt metal, and you want to use it for that.
bowakowa7 years ago
I've run into this same problem. I've been scouring the goodwills for cast iron.
try this.
For a crucible, either make one out of fire clay or get a block(s) of graphite (eBay's usually a good place to look). You can also find graphite crucibles that have already been made on eBay, but they usually go fairly high in the price range as the auction progresses.

As far as slag goes, you'll get quite a bit of slag, but if you can find some bailing wire (needs to have carbon in it) some where around you, you can just dip a piece in and the slag will attach itself to the wire.

Here's a Crucible site that can help you figure out what you want/need.

Almost forgot, there's also Carbide Crucibles and there's a powder (flux) that you can add into the crucible while you're melting the cans to make the slag float to the top so that you can just scoop it off. Here' a site with more details (I saw the powder on eBay sometime last year, but am unable to find it now).
Goodhart7 years ago
Aluminum, untreated (which it would be once heated at that temp) oxidizes fairly quickly, and under that heat, even more so.

Some technical info on Aluminum Oxidation rates...