Introduction: Flowerpot Furnace - a Home Foundry
In this instructable I'm making a classic flowerpot furnace, so called because its shell is a terracotta flower pot.
A flowerpot furnace is a fairly cheap and easy way to make a furnace for home/hobby melting of metals such as Brass and Aluminium.
In a flowerpot furnace you can melt down scrap brass and aluminium to use in various ways, such as: sand-casting, lost wax casting, free-casting or just to get your scrap/recycled metals into a more convenient billet.
- Large terracotta pot (mine is about 800 mm diameter)
- 1 x 25 kg bag of fire clay
- 1 x 20 kg bag of Portland cement
- 1 x 1 kg bag of perlite
- 1 x 3" diameter steel pipe
- 1 x 400 mm plastic plant pot
When I made my furnace, I was living on a 4 acre property so I didn't have to worry about smoke or noise ... if you are in a more urban area, you should probably consider your neighbors.
Step 1: Make Your Form
I started with a large terracotta pot (800 mm diameter) and drilled and chiseled a hole in the side for my air intake pipe. The steel pipe that I used was an old piece of steel tube fencing that I had lying around on the farm. What you are looking for in a steel pipe is something that you can attach to the outlet of your vacuum cleaner. I had to make a custom connection for my vacuum as it didn't have any. Oh, and the vacuum, I bought as a second-hand throw-away for $5.
Mix the fire-clay, cement and perlite together in a large tub (or in a wheelbarrow). The mix that I used was 1:1:5 fire-clay, cement, perlite. The dry mix was turned over and thoroughly mixed together. Make a well in the middle of the mix and add in about 3 liters of water until it is a stiff mortar-like mixture.
Put about 3" of mixture into the bottom of the pot (to the bottom of the air-hole) and pack it thoroughly. I used a steel rod to pack it down and make sure that I got all of the air bubbles out.
Put the plastic pot into the center of the terracotta pot and put your air pipe into the hole. Pack the wet mix around the air pipe ... again, avoiding air bubbles.
Keep adding more of the mix into the void between the terracotta pot and the plastic pot while packing the mix as you go.
Bring the mix up to about 2" from the top of the terracotta pot and smooth it down as much as possible.
Now, you want to put a garbage bag over the pot and leave it to cure. I left mine for a week, but then, I was busy.
Step 2: Remove the Form and Fire
When the refractory is cured, remove the plastic pot from the furnace. The pot was a little bit stuck in my furnace, so I used a sharp knife to convince it to come out.
I left the furnace for another day and then, on Sunday ... I cooked it.
Filling the furnace with tinder and then putting some fire to it, I kept the furnace cooking for a good four hours. You need the fire to heat the refractory without being hot enough to make it expand. This means, basically, a fire that about 1/2 fills the void and let the ash build up. The ash is an insulator and it helps to keep the heat inside the pot. The idea for the cook is to drive the last of the water out of the refractory so that when we really apply the heat, you don't get pockets of water vapor that will want to escape quickly (e.g. explosion). Slow and gentle is your friend.
You can go back and do this as often as you like ... safety first!
Step 3: Fire in the Hole!
Finally, it's time for some heat!
Put some oil soaked paper into the bottom of the furnace (near the air hole) and charge the furnace with coking coal, coke, briquettes, whatever you are going to use when you get this baby cooking.
Light the paper (using a lit stick, straw or a long match) and get the fire going. Let the fire catch well and then insert the air-pipe into the air-pipe-hole and attach the air-pipe to an air supply (for instance, the exhaust of your trusty shop-vacuum). Start your vacuum on as low as possible so that you don't put the fire out.
When the fire is thoroughly going, increase the power on your vacuum.
When mine is going, it sounds like a jet engine!
When your furnace is hot enough, you can lower a crucible filled with scrap metal into the furnace and let it cook.
When melting aluminium, it took about 20 minutes to turn 1 kg of aluminium into liquid.
This is when you need to have a steel scraper to remove the oxidized aluminium from the top of the melt. If you have a degas, you would add it after you've de-scummed the melt.
Of course, you have some fire-tongs to remove the crucible ... don't you?
ALWAYS wear closed shoes of a sturdy leather construction. DO NOT WEAR THONGS ... DO NOT WEAR SANDSHOES
ALWAYS wear a leather apron
ALWAYS wear elbow length leather gloves (welding gloves work well)
ALWAYS wear eye protection
ALWAYS work in a well ventilated area
ALWAYS tell your wife that you DID all of that!