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Mini Charcoal Furnace

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This is the first 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 hopefully in the future I will make a bigger and better furnace.
It's easy and quick to make, I will show in this instructable the steps on how to make it using materials some of us have  in our house. The only "big" money might be the refractory materials and characoal.

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.
The furnace tools I made from a 5mm construction rebar, can of beans and old bathrooms hooks.

In the near future I hope to add to this instructable a few images of my first sand casting.

A few Saftey words: Coming  into contact with fire and boiling melted metal can be very dangerous so always work safe using proper full body protection including respirator mask against toxic fumes and dust from mixing refractory materials. Never melt in a wet area or near water, if water comes in contact with the boiling aluminium it might "blow" in your direction.
 
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Step 1: Furnace construction

A bit of form work: check if you have any scrap plywood, MDF etc'  to hold the refractory furnace shape.
I used scraps of plywood, MDF, chipboard, soft wood, cardboard all screwed  together.
Start with the walls and the base. Optional: making small wooden angles for the corners will make the corners flat  preventing them from breaking.
Drill a hole 2" from the base using a core bit for timber.  The diamater of the hole should fit the size of the pipe you will use for the blower.
I used a cardboard pipe to form the opening for the blow pipe.

You can smelt aluminium foil. Just take a large square and fold as many times as you can. Then compact it by hitting it with a rubber mallet.

freeza361 year ago
What would you use the ingots for?
jstnb1 year ago
Add something like a piece of 2x4 on the muffin tin, before you start hitting it, this protects the tin, but does deliver the impact.
Kaiven2 years ago
How do you get the ingots out of the muffin tin? Haha, I have 6 stuck in the tin and I can't get them out.
myakka Kaiven2 years ago
hammer time...
Kaiven myakka2 years ago
Broke the muffin tin.
hello,

i am sure i read somewhere that if the inner refactory mix is not to thick, and then surounded by a layer of sand (allows expansion) or probably ceramic wool, then a further layer of refactory insutation, then a expandable layer (you get the onion ring effect idea) then the refactory layers are allowed to expand and contract without too much stress and therefore cracking. i think some experimentation is needed.

to hold the solid layers together(at the top), some wire netting, or stainless steel wire in a zig zag fashion around the circumference (binding)between the layers would bind the whole lot together, whilst allowing expansion,

just food for thought
jspencer172 years ago
How many melts did you end up getting out of your refractory mix? How about the second forge that you constructed and posted more recently?
lpdunwell2 years ago
awesome instructable!!
only one thing that could remove confusion: add something to the images to compare size, like a pet bottle or so. i thought this thing was tiny, but obviously it's not XD
tincanz2 years ago
Great instructable, but I wonder: what will you do with the ingot? will you make it into something useful i.e. a nutcracker :-), or will you just have it lying around? If you make things, you should do an instructable for it.
jbend3 years ago
can you use wood insted of charcoal.
tincanz jbend2 years ago
I don't know about Aluminum, but for Iron, wood isn't hot enough. Its easy to make charcoal, though. just heat up wood in a container (maybe a can) over a fire. With the right temperature, the volatile gasses leave the wood without igniting, and the wood blackens, becoming charcoal.
_Scratch_3 years ago
How many nutcrackers do you have??
Lambskin3 years ago
Can you melt copper with it?
g.petinati3 years ago
Regular portland cement takes almost a month to cure completely. Refractory cement cures at a considerably shorter time, but let it cure for the time indicated on the package (or at least a week) before you remove the frame. This may prevent the concrete from cracking.

After 2 or 3 hours from the pouring of the concrete, put a damp cloth over the top of the furnace. Keep it wet the whole time and protect it from wind, wich will dry the concrete. If the concrete dries it'll be a lot weaker.

Congrats for the great instructable.
Nice instructable, paracord!

I'd like to make you notice though, that you are not in the SAFE side!
You should operate on a bed of dry sand, not in proximity of a wood house
and on a not so dry soil.

If the melted metal drops to the soil it will instantaneously "explode" due to contact with moist/water on the soil and it would spray around spliters of melted metal.... mmmhh, I guess you dont want that!

I'm sure you have read suggestions and advices in
http://www.backyardmetalcasting.com/

Be careful.

NutandBolt (author)  undinstructable3 years ago
Thank you for your reply and concern, I was wondering for some time who will win the "jackpot" and ask about the wooden structure on the side or the concrete slab beside the furnace or not having a nice big sand box under my work area, You are the winner.
Correct all above should be taken into consideration when working with molten metal.
Not that it matters but I work with full body protection so even if aluminium will "explode" no risk to me.
This specific MINI furnace I made Poses no danger to the wooden structure being caught on fire, I was working with charcoal (Easy to control) not waste oil (hard to control/on fire).
I have my water hose ready and no I won't water the molten metal.
Safety First ;-)
very nice instructables! i started making a forge about threedays ago the crucible i made is a 5mm steel oxygen bottle an the forge itself is an old propane bottle( the one i used is about 50cm in diameter)
NutandBolt (author)  didgitalpunk3 years ago
Hi thanks for your comment, I think you made great crucible I was using beans can for my first few melts and that is a bad idea although I got away making a few ingots befor holes appeared. So 5mm thick steel sounds great. I am in the stage of scraping my furnace and making a proper one with proper refractory using the same old propane gas tank as you are planing to use. Regarding the paint don't worry about all the impurities once you get your high tempature and the aluminum is ready to be poured you just have to remove all the slag with fork or some other great instrument. It would be great if you can post a few images of your crucible/furnace. Thanks again :-)
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thanks for the tips! yhea i'll try to post some videos of what i did but it'll take about two weeks but i wont forget! thank again!
ho yeah i forgot. if you put aluminum with paint on it, does the paint burn and desintegrates or does it form slag? thnksfor answering!
i made one similar to this it it gor hot enough to melt salt and glass and even small amounts of steel
abraxsis4 years ago
FYI, mixing black furnace adhesive/caulking with pearlite (a soil additive) is an EXCELLENT refractory material, not to mention very cheap. I used this inside a large coffee can for a small foundry when I work with larger quantities of silver than my blowtorch/ceramic crucible can handle. After a few partial fires (im big on tempering any refractory material at least 4 times before bring it to full temp) I was able to bring a coffee can foundry to a point I could melt small amounts of copper, which melt. closer to 2000 deg. F. Also, something to mention. NEVER ... EVER ... get molten metal on concrete (like in a driveway/basement/etc, the higher moisture content can cause a violent steam explosion which throws concrete shrapnel everywhere. ALWAYS try to use your foundry on the ground or use something like old drywall (the gypsum it is made from is nearly heat proof) as a "floor" under your melting/pouring location.
blkhawk4 years ago
Have you found any practical use for molten aluminum ? Do you think that machine parts could be made melting aluminum this way?
NutandBolt (author)  blkhawk4 years ago
I have a lot of ideas for sand casting and I am still pilling my aluminium ingots for the next projects. You can duplicate almost any object you can think of. As far as I know engine pistons are made from aluminium so my guess is they could be used as machine parts but again I am no expert and I am not going to duplicate machine parts in my tiny aluminum furnace ;-)
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Chainfire4 years ago
what were the dimensions,and how refractory did you use?
 Would reinforcing the concrete with rebar or chicken wire possible help with the cracking? How good of an insulator is the concrete? Would Sakrete possible be a better material to make the forge out of than concrete? Its meant to be an insolator. Could it handle the high tempatures? Also, not fully related to this instructable, just a question about firebricks. If you used the insolator firebricks, could you cover them with tiles, like leftover bathroom tiles, because apparently insulating firebrick is very soft, would the tiles be able to take the heat or would they crack?
NutandBolt (author)  snowluck23454 years ago
I'm not an expert regarding aluminium melting but I will try to answer your questions after my little experience with my furnace.
* I do think that chicken wire or small rebars will help against cracking, I didnt use it in my furnace and it cracked.
* I don't think concrete is the best insolator although I got very quick meltings using my furnace. The aluminium was melted in less then 20 mins.
* It cracks under high temperature but you will get a few meltings before the furnace will die.
*My next experiment is exactly what you are asking, I was thinking too that the tiles will take the heat but I have a feeling they will crack.
I will update my instructable if the experiment will work.



Try clay and Iron Oxide mix bake it with a small fire before using the blower and try a melt
Tiles will crack if you get them hot enough. fireplace mortar maybe? Or use some of the homemade refractory recipes on the net. http://www.backyardmetalcasting.com
x z i t4 years ago
i made an ingot before but completly out of soda cans. you just need to remove the paint from the melted aluminum with a fork
NutandBolt (author)  x z i t4 years ago
I was thinking of melting aluminium cans the only thing I read on many sites is that the cans produce a lot of a slag. How many cans do you think I  will need to get a few ingots  (muffin tray size)?
it takes about two cases of cans witch is 48 cans to get a little over a pound good aluminum. I done foundry work for 15 years of my life. by the way aluminum melt down at 1500 Deg and is pored around 1550 to 1600 Deg depending on the casting being made.
it's really not a big deal if you are just learning and pouring ingots. just remember to scoop the slag off last, not continuously.
Fred826644 years ago
this is a good way to melt down a lot of beer and pop cans or hard drive bodies and platers
coppeis4 years ago
Yes but what else can you make with aluminum?
NutandBolt (author)  coppeis4 years ago
After removing the slag (impurities) and making the ingot, you can re-melt them and make duplictates of almost every shape and object you can think of by using the sand casting method. Or you can just use it as a paper weight...lol
greenfreak4 years ago
dude! this is great!.... im gunna build one when i get some more cement! and im gunna use a metal box to keep it more sturdy!... thanks so much for the instructable!
NutandBolt (author)  greenfreak4 years ago
You are welcomed, My next furnace I will build in metal box too. I agree it's much more sturdy. If you do build one post some images.
alright man! will do...
zcshiner4 years ago
I have seen other furnaces put the blow pipe on the side of the wall vs the center, so it swirls the air (cyclone) instead of just pushing it inside. Think of a squirrel-cage blower, and where the nozzle on that is placed.
NutandBolt (author)  zcshiner4 years ago
When I built my furnace I was contemplating rather to place the blow pipe hole in the side or center. I found one site that said to place pipe in the center for characoal furnace and side for gas brurning furnace. Perhaps placing it on the side is better, to be honest I'm not sure which is better ...
ld2i4 years ago
Very well written, one of the best furnace/forge articles I've read. I'll be sure to try this once I get my hands on some materials. I have a couple of questions though if you would be so kind: Is it possible to use normal cement, or does it have to be the special refectory cement? And also, would this work to melt aluminum cans as well, or would those just disintegrate?
NutandBolt (author)  ld2i4 years ago
Thank you very much I appreciate you positve comment . If you use normal cement the furnace will probably crack. As you can see in my last images after a few uses.
You can place the cement in some metal container, the container will probably prolong the furnace life. You can google furnace refractory mix and you will see many sites that provide guides for the proper materials and mix ratio.
Most people start by melting cans the only thing is you need a lot of cans to get some decent amount of molten aluminium. And the cans produce alot of slag that have to be removed.
I would recommend melting some aluminium objects that you have no use for they will give you more molten aluminium.
ld2i NutandBolt4 years ago
Ah, I see. I'll look into that then. Thanks for the help, I appreciate it.
Ichmawida4 years ago
what are those ingots used for?
NutandBolt (author)  Ichmawida4 years ago
The ingots are (almost) pure aluminium after removing the slag, you can re-melt them and make duplictates of almost every shape and object you can think of by using the sand casting method. Or you can just use it as a paper weight...lol
pkmn NutandBolt4 years ago
(removed by author or community request)
munson pkmn4 years ago
slag is just impurities in the metal such as small amounts of iron
NutandBolt (author)  pkmn4 years ago
Slag, dross and I am sure we can find a few more names for all the impurities floating on the top of the molten uluminium. Basically all the crap we have no use for and have to be removed from the molten metal.
seems like a fun thing to do. I'll try it Thanks!
pudi.dk4 years ago
Great instructable. One advice however would be to insulate the inner walls with vermiculite board which is pretty (very) fireproof, used in burning stoves. I'm planning a furnace made with an old propane tank (carefully emptied, punctured and cut) to reinforce. It's going to be with propane however, which will be easier to work with. I've tried charcoal in the past and it's a PITA controlling the heat and the placement of the crucible.
Great furnace, well made! A very good instructable. The only thing I'd do differently is use a better crucible, bean cans burn through easily and can start leaking molten metal at the worst possible moment (speaking from experience) :D Old oxygen/c02/fire extinguisher tanks make good crucibles
NutandBolt (author)  scraptopower4 years ago
Thank you, I am all ready plotting ideas in my head for my next furnace I will definitely have to make better and bigger crucible. Getting molten metal on myself is realy not something I want to try. lol
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