Aluminum Foundry
Intro: 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.
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.
STEP 1: Materials
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
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
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.
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
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.
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.
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.
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.
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.
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.
22 Comments
leif_evans 6 years ago
Kellyg124 7 years ago
neffk 9 years 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.
kidharris 12 years ago
neffk 9 years 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.
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