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Picture of Aluminum Foundry
After going through several different designs on the internet, a friend and I decided to make our own Aluminum foundry of a custom design. This instructable is more of a record of experimentation with an (eventual) successful outcome as opposed to a step-by-step with little trial and error.

Be sure to carefully examine each photo and read the highlights, the majority of this instructable is explained and documented in photos. Any and all questions will be answered to the best of the ability, and if we don't know we'll do our best to find out.

This forge is a bit more durable, but much less portable than other models you may have seen, but it can also melt steel should you choose to buy a proper clay-graphite crucible. The ability to melt steel is given to the furnace by adding clay/brick walls to the top of the furnace as seen in step three, no extra equipment (aside from the mud/brick and crucible) is needed.
 
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Step 1: Materials

Picture of Materials
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Materials
2" Steel nipple
2" Steel end cap
Briquette charcoal
Charcoal starter
Charcoal starter fluid
Aluminum (Cans/Scrap)
Blow Dryer
PCV pipe segment (~1.5" diameter)
Groove-joint pliers
Slag stick (A long bolt will work)
Proper safety equipment (eye protection, welding gloves, etc.)
Optional
Mud/clay
Small shovel
Ceramic Mug
Soup Can

Step 2: Construction of the furnace

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For this step, you'll need:
Charcoal Starter
Charcoal
Mud/Clay
Blow dryer
PVC pipe
Duct Tape
Small shovel

First, dig a small depression to sit the charcoal starter in, using the mud cover up all but one of the holes in the bottom. Fill the starter approx. 1/2 way with the charcoal. Take the blow dryer and duct tape a length of PVC pipe to it. Stick the end of the PVC in the one remaining hole and set the blow dryer on a brick or something else to keep it directly off the ground. Center the crucible (more on that later) in the furnace and fill in the sides of the furnace around the crucible with more charcoal. Soak with starter fluid and light a match.

We tried using a clay flowerpot but it cracked minutes into the first burn of the furnace. Not 100% on what happened there, either the pot wasn't completely clay, it wasn't properly fired, etc.

Step 3: Problems with the Ceramic/Soup Can crucibles

Picture of Problems with the Ceramic/Soup Can crucibles
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Ceramic
The first crucible (a container used to hold the molten metal) we tried was a ceramic mug with the handle broken off. This lasted about 15 minutes before cracking, however because the coals were packed around it, the mug retained its shape, so at the end of the night and after melting ~20 cans, we had a good chunk of nearly pure aluminum in a puddle under the furnace. The slag was retained in the bottom of the mug, unable to pass through the cracks.

Soup can
Following the instructions of other instructables and misc internet resources, we tried a soup can next. The soup can worked for a brief time of ~10 minutes before becoming extremely brittle. It broke while tapping the bottom of the can with the slag stick to try to get all the molten aluminum and slag out.

Step 4: Steel Crucible

After the first two crucibles failed, we settled on using steel. A steel end cap and nipple with a 2" diameter was our choice. This worked for approx. 30 minutes before the end cap completely melted off and mangled the end of the nipple. We determined the cause of the too-high temperature was due to the high wall of insulating mud and brick, instead of just covering the holes, the wall was up to the top of the furnace.

We salvaged the nipple by turning it upside down and purchasing a new end cap. After heating it red-hot and using a hammer and chisel to knock off as much garbage as possible, the crucible was serviceable again. We also pounded a pour spout into the nipple for ease of filling smaller molds.

Its also interesting to note that when the steel was first placed into the furnace, it burned green. We believe its was the zinc used in the galvanization process that was causing the flames to turn green.

Step 5: Melting, pouring, and removing the slag.

Picture of Melting, pouring, and removing the slag.
After reconstructing the crucible and rebuilding the furnace with a much lower mud wall, the steel crucible performed flawlessly. A free and easy way to create ingots (casting of a simple shape which can be used for hot working or remelting) is to simply take your fingers and bore a trench in the dirt, then pour the molten aluminum in.

An easy pouring technique: Using the groove-join pliers, pull the crucible out of the furnace and set it on the ground. Open the pliers all the way, and grip the crucible around the middle of the nipple. This will allow you to turn the crucible all the way upside down should you wish. Of course, its best to wear gloves and eye protection during this time especially in case it splashes/other bad things happen.

Using scrap aluminum found around the dump or in the nearby woods as in our case, gives a much higher gross of aluminum with a lot less slag than soda cans. Go to your nearest dump/landfill/etc and get some scrap aluminum.

Slag is the non-aluminum material left over from melting down the aluminum. It could be other metals with a higher melting point, minerals, etc. The point is, is that it needs to be removed. Luckily for us, slag floats on top of the molten metal, so one takes the slag stick with the pliers, and scrapes the slag off the top of the pool of liquid aluminum. You'll know its slag because as it cools, it turns a dark gray color, whereas the aluminum will be shiny and bright.

Step 6: Final Remarks

One thing that cannot be stressed enough, you're working with molten metal and extremely hot temperatures. Gloves, proper eye protection, long sleeve flame resistant (aka, not underarmor) shirts, jeans, boots, its all necessary. Keep water away from the molten metal, if water were to directly contact the molten metal its *possible* that the sudden expansion of the steam could cause a small bubble-popping like effect and splash the metal out of the crucible.

Soda cans are not as horrible as most people say. While its true they contain a bit more slag than most other scrap metal, its easily removed, and after being melted down a second time to try to get rid of even more slag, they were reasonably pure. In short, for someone just starting out melting metals, soda cans are great. They're free, melt quickly and easily, and when you end up wasting 30 of them experimenting you don't feel bad about it.

When collecting scrap metal to melt down, be sure that you can actually fit the piece of metal into your crucible, or have a method of breaking it down. A dremel is invaluable in this aspect, with a cutting wheel and about ten minutes, I had a three foot piece of solid aluminum pipe broken down into manageable pieces. The little rubber/plastic caps on pipes melt easily enough, however the screws/rivets need to be cut out of the pipe (again by use of dremel) otherwise it turns into unnecessary slag.
neffk3 months ago

First of all, congratulations. You melted steel. That's awesome.

Second, you've fired your foundry to 1400 oC. Aluminum melts at 660 oC. The aluminum ingots you poured look a little dull which may indicate that you heated the metal too high (if the internet is to be trusted). Maybe turn down the air or something to reduce the heat output of your fire.

I wonder why your steel crucible failed. Others have had success for several pours with similar setups. Are you heating the crucible without scrap in it? The aluminum evens out the heat when it starts to melt. For example, when I melted down some 3xx aluminum the other day, the cast-iron crucible started to glow at first but then the aluminum melted and the pan turned black again. Well, with the sun shining, it looked black. When I did another session in the evening with much lower light, the pan glowed a little with the aluminum melting. Point is, aluminum spreads the heat around in the pan.

The proper method, of course, is to use a pyrometer to measure the temperature of the molten aluminum. I don't have one so I'm using a trick I read about on the internet which is to watch for the last piece of scrap to melt, then count off so many seconds, then withdraw the crucible. For my setup, with a gas forge, it's about 30 sec. Another method us to go by color. If you look on the chart you'll see that a dull red is 650 oC or so.

Third, I used a cast-iron pan, about 10 $ at Wally World. I had gotten a 2" x 5 pipe nipple and cap before and the price was about the same. Problem is that you have to break the aluminum into tiny pieces to get it into a 2" pipe. The pan was a lot easier. I added 2' of angle to it with some 1/4-20 hardware. (Check out http://mikegigi.com/meltmetl.htm for more hints. That guy is hardcore.)

Forth, make some green sand. So easy. Just get some sand (must be dry) and some clay. Add a little water and mix, mix, mix. I used fire clay but you can use other stuff, like ground-up kitty litter or bentonite. Then you can make any shape you want. I used a small paint can to make nicely-shaped ingots. It's so easy and I wish I had learned how to do it a decade ago.

Fifth, figure out how to make your setup convenient and reliable. It's easy to work on a project when you're inspired and curious but what if you need to cast something out of aluminum to solve a real-life type problem? I know it's a hobby and you're doing it for fun but why not capture the knowledge that you've acquired so you can do it again at the drop of a hat? Just a thought, Mr. Fox.

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kidharris3 years ago
You should not use galvanized steel for any thing to do with a furnace. At high temperatures the zinc burns off and emits zinc fumes which are extremely harmful to your health, including death. Same problem with welding galvanized steel. Lots of info on the net, read it.
neffk kidharris3 months ago

I'll second this. If you can SEE the green, it's bad. People report terrible symptoms from just a little exposure from welding galvanized steel and that's without enough to be visible.

lol loved the last bit, I was working at my homemade forge melting aluminum with short sleeves shorts. really good ible tho. if anyone needs a good hot fire hook up a shop vac to it works like a charm.
curvy773 years ago
lol depending on how hot your forge is slag will not float. my forge gets hot enough to melt cans but not to completly reduce them to a liquid state. (i use wood. pine mainly) so too get my aluminum i take a stick one all my cans are gone and press the slag looking junk in my can. and wha la! liquid aluminum sqeezes out like water from a sponge.
bahi3 years ago
Nice instructable, It covers lots of real life problems involved in homemade foundry, thanks.
All cotton and leather clothing are definitely important when dealing with fire, no synthetics.
Not having frayed edges on your cotton coat is a plus also. I had an old carhart on once and it got a little warm and I was pretty surprised to find the front of my coat on fire. It did get rid of the frayed edges.
yep, i agree with hailsteve. I'm a blacksmith and sometimes i will burn the zinc off of a galvanised piece of steel and that burns with a bright cyan(blue) colour. Love your little furnace though. It's just the very thing. Ps i think the big foundries use a clay crucible. All the best smithy
2k4u6 years ago
You probably saw my instructable. If your soup can broke, it's too hot. They should always last for one melt, no more though. It's good to get a hair dryer with a low and high setting. Crucibles...Once you start REALLY melting stuff, soup cans won't cut it. Go to Home Depot or Lowes and go to the plumbing section, and get some large diameter iron water pipe, I think they'll cut it for you. Since they don't make caps that size, weld some steel plate onto the bottom. But I understand some people can't do that. I just use a $50 Oxygen/MAPP thing that every Home Depot sells, it runs on those little 1lb. cylinders, which leads to the next thing. These are crucibles every can have that last for quite a few melts. Go to any hardware store or even Wal-Mart, and get some disposable propane tanks. Not grill size ones, but the ones used for camping stoves and torches. I don't even empty mine, I shoot them twice with a .22 pellet gun to penetrate the tank, let it all empty, and use an angle grinder with a cutting wheel to chop the top off. The bottom leaves you with a nice crucible. If you can't use an angle grinder, just hacksaw. It's slow, but it works.
PKTraceur 2k4u6 years ago
Camp stove propane tanks are a good bet, I just melted some aluminium, however my heat wasn't high enought die to the fact that all I used was maple wood... Dont worry, I added a bunch of black coals from the previous fire. I suppose im going to have to get some charcoal... -PKT
Ben.land1016 years ago
i did the same sort of thing but instead of charcoal i used kindling and it took a long time and a lot of sticks but it worked just fine
trf6 years ago
alright if u want a crucible that will last....go to a ceramics shop and make your own cone 7 or 07 i forget which 1....it will last quite a few melts the only issue being that it needs preheating
khaeotixs6 years ago
i wouldn't recommed casting into dirt. it may contain small spots of dampness/wet or just be a tad too cold and lead to a reaction with the metal that is effectively an explosion of molten/semi-molten metal. i only had this happen once, and since then i found a brick with a V in the top of it. i heat it in the forge for half a minute or so to remove any possible dampness, then place it to one side for casting into. hope this stops someone ending up with burns like mine were ;)
hailsteeve6 years ago
I don't think the zinc made it burn green. Copper is the chemical that burns green, so maybe there was copper powder on your pipe or something.
Salaric6 years ago
Our furnace runs with a propane cylinder and a bullfinch blow torch attachment - this works really well. (its made in a galvanized bucket with perlite and fire clay around the inside - galvanised buckets must not get to hot on the outside as the galvenising vapourises and the fumes are toxic - were working Mk 3) On a safety note of my own - pouring should never be done over concrete as if the molten Al hits it, it evaporises the water in the cement causing an explosion. Value cup cake tins make good ingot trays we found. If lots of air gets to your melt it will oxidise directly causing lots of slag to form - putting glass in to form a protective melt layer on the top can help along with the actual design of the furnace.
mr.space6 years ago
my god... i dug a hole in the ground and put some coal in it, got a cast iron pot and put in in the hole... it wouldnt melt anything so i got a balloon blower and a copper pipe an put it in... melted the aluminum AND THE CAST IRON
tacamaral6 years ago
The explosion thing happened with a friend of mine. Luckily, he only had some burn scars on his belly and leg, and his son lost some hair. Another thing I believe you could try melting: old carburators. They are an alloy of tin and lead, I think, with something else added. They're tough, look like steel, are way cheaper (junkyards) and have a lower melting temperature. Well, at least in Brazil they're easily found. : )
From your picture it looks like you had a bit of an issue with impurities in your melt. You can saw/file off the outside of these and then use them as a starter for your next melt. For my latest melt I used old harddisk cases which made for much better results.
IdahoDavid6 years ago
Heed the safety caution cited here. Several years ago I was involved in salvaging the lead from logs used on a Scout rifle range. Lead melts at a considerably lower temperature, but in its molten state is pretty nasty stuff. We were creating lead ingots by pouring the molten material into small trenches scraped into the dirt. The solidified ingots were then dipped in water to cool. An ingot I was working with overflowed its trench and I dipped the misshapen lump in the water and without thinking put it back into the melting cauldron still wet. The resulting explosion of melted lead left my face spotted with numerous burns and my Scout shirt with several holes. (I was lucky it didn't burn my eyes.) It is amazing I survived my teen years!