My first Mini (disposable) Charcoal foundry.

This is the first disposable charcoal furnace that I built its purpose melting small amounts of aluminium into ingots or sand castings for small objects. I don't predict a long "shelf life" for my furnace before it will start cracking but I will get a few melts before I scrap it, This is just a prototype and in the future I will make a bigger and better furnace.
A few details about my furnace: I made it all 2" thick around including the furnace lid. I used Plywood, MDF, cardboard, chipboard all left overs from other jobs to make the furnace form.
The furnace tools I made from a 5mm construction rebar, can of beans and old bathrooms hooks.

To shape the furnace core I used an empty plastic can of paint. Cut it to the desired diamater leaving space for the charcoal / crucible and at least 2" to fill the refractory for furnace walls. Using masking tape to hold the can diamater shape makes it quick and easy to remove after your refractory is dry. Make a hole for the cardboard pipe or just tape the pipe to the can to prevent blockage of the opening. I used 10mm MDF cut to fit the plastic can diamater. It is important to cut the MDF into half this will help to take it off in later stages without breaking the fresh refractory. Make another 2 circles and screw them all together. Use the left over materials from your cuttings and attach them together. Use any flat scrap for the base. Place the cardboard pipe in the centre of the lid for the vent opening.
Strips of 5mm MDF will do for holding the rebars in place and will be very easy to snap off in the stripping stage. Screw the MDF into place, mark the hole positions and drill the holes.
I bent 5mm rebars to serve as handles for the lid. Place the handles in the holes and leave a 20mm gap from the base.

Refractory: The mix of materials chemically and physically will help hold furnaces high temperature avoiding thermal shock (in plain english, cracking).
In the image you can see 2 bits of ply attached to the inside walls of the furnace, they will be stripped of later and the gap left in the material will be a good handle grip for lifting the furnace.
Start from the base of the furnace and drill the copper pipe to the base center point, after that using a block of timber etc. compact the refractory and remove of all unwanted air bubbles.
Drill the center screw out and leave the copper pipe in its place. Attach the plastic can with the same screw in the center over the refractory.
Cover all sides around the plastic can with the refractory mix and compact as you go.
When you get near the top place the cover and secure it with timber to the furnace plywood walls.
When all is compacted well and covered use a hammer to tap on the plywood sides to get rid of any remaining air bubbles.
The refractory I used for this furnace was just cement+sand+fireclay and a small amount of water just turning it into a nice paste. When mixing all materials use gloves and respirator.

I knew It will probably crack at some stage but I got a few nice meltings before that.

It is a very important thing to remember: PATIENCE let the refractory dry don't be hasty to remove the cover or you will crack and break it, all your hard work will be for nothing.
Start taking the screws out and removing the sides of the furnace, you can use a chisel or such but don't wedge and pull it against the furnace.
The cardboard can be taken out with one finger, once it is wet it wont stick.
All the scrap you can throw away or use to make another furnace.

Foundry crucible, The professional ones are made from different materials such as clay graphite, silicon carbide and more. They can be purchased from as little as a few bucks to couple of hundred.
The crucible I used is worth about 2$ - bargain..he..he.
I made the crucible from a used can of beans v shaping the lip for easy pouring, I drilled 2 holes to the sides of it and placed 2 bolts to act as lifting pins.
On the bottom I tied steel wire with a loop at the end.
The lifting fork and hook I made from 5mm construction rebar that I welded to an unused bathroom hook.
I also bought a 94c muffin tray (another bargain) to make some ingots.
The rebars are long enough to keep a safe distance from the boiling aluminium and your body.

We had great weather for a BBQ and a good opportunity to try my furnace. After lighting the BBQ coals I took a few and placed them on the base of the furnace and around the crucible. I used an old vacum cleaner pipe and taped my wifes hair dryer to one end after sneaking it out of the house. Later on she saw her hair dryer was attached to my furnace and lets just say I won't do it again. I placed the door handles and the locks without the nut cracker (no room in crucible) into the crucible coverd the top with the lid and turned the hair dryer on (low). I think after about 10 min I turned the dryer off, removed the vent block and looked into the lid vent hole and saw the aluminum handles were gone, for a moment I tought nothing melted but then I skimmed the scrap from the top and it looked like it was melting. I left it on for a few more minutes and I took off the lid used my DIY lifting tools and got all excited to see that liquid shiny as a mirror coming out into the muffin tray and forming into my first aluminium ingot.

This was a fun experiment !!! Now Some conclusions
As I predicted my furnace started to crack after more meltings. Before it will "die" I hope to get a small object sand casting. And after that I'll scrap this furnace and make a bigger and better one.
I don't recommend using tin cans at all, it can be dangerous, I got a few ingots out of it but one corn can I used broke inside the furnace with big holes.
Metal crucible should be made from thick steel, tin cans break very easily.
I also think refractory in a metal container such as empty gas cylinder will crack less.
This was a great experiment for first time aluminium melting.
This is a short video I made, I know its not great and my hand is in the way and a bit of dross fell into the muffin tray but it gives the general idea of ingot making.
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