July 23, 2017 | Author: zaphoss | Category: Refractory, Foundry, Concrete, Ingot, Casting (Metalworking)
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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


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.

Step 2: Furnace core

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.

Step 3: Furnace top

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 (marked red lines in images) and screw them all together.

Step 4: Furnace lid

Show All 7 Items 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.

Step 5: Furnace Refractory

Refractory: The mix of materials chemically and physically will help hold furnaces high temperature avoiding thermal shock (in plain english, cracking). In the third 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. (I will not go into details regarding the mixing ratio of refractory so if anyone wants to make somthing similar that will last longer check other sites for proper refractory materials mixing and exact measuring ratio's). I just used cement+sand+fireclay and a small amount of water just turning it into a nice paste. It will probably crack at some stage but I'm sure I will get a few nice melting before that. I also recommend placing a wire mesh between the core and furnace walls that will help against cracks.

Step 6: Removing furnace frame

Show All 18 Items This 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.


After the refractory is cured it is time to fire it up.... While waiting I did a bit of aluminum experiment to cheak how hot it gets using my multimeter, nut cracker and camping propane cooker. In the images you can't see the flame but look at the temperature (celsius) on the multimeter screen The nut cracker melted in less then 5 min.

Step 8: Furnace tools

Crucible: Is the container that holds the aluminium parts before melting them and for casting them in sand or just into an aluminium ingot. 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 in this instructable is worth about 2$ - such a bargain..he..he. In retrospect: 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. 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.

Step 9: On the menu

I looked for some aluminium parts in my house and found a few handlels and a nut cracker. So I decided its time to "feed" my furnace.

Step 10: My first aluminium ingot

Show All 14 Items Last sunday 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 had everything ready and even a water hose (for characols only not for the melted aluminium) in case of emergency . 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. 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, I just saw dark slag on top, 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.

Step 11: This was a fun experiment !!! 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. This was a great experiment for first time aluminium casting. Hope you enjoyed my instructable. This is a short video I made, I know its not great and my hand is in the way and a bit of slag fell into the muffin tray but it gives the general idea of ingot making.

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fynn.oconnor1 month agoReply You can make your charcoal by simply burning wood in a very low-oxygen environment. In Zambia the charcoal burners pile up wood then cover it in mud and let it burn. You can even make stoves that burn the gas wasted in this process ( low smoke, and your residue is usable charcoal.)

blkhawk4 years agoReply Have you found any practical use for molten aluminum ? Do you think that machine parts could be made melting aluminum this way?

fynn.oconnor blkhawk1 month agoReply Yes i think machine parts could be made but don't forget aluminium isn't very strong or durable as far as metals go. I doubt they would last long at all. Honestly you're only limited by your imagination. Im planning on making some throwing axes out of the aluminium that melted of the machines in a fire at our sawmill.

NutandBolt (author) blkhawk4 years agoReply 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 ;-)

freeza362 years agoReply What would you use the ingots for?

ATMorris5 freeza366 months agoReply smelting the aluminum into ingots makes the metal easy to store for later use, and you can melt them down to cast aluminum objects.

steampunkpotato8 months agoReply 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.

jstnb2 years agoReply 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.

Kaiven3 years agoReply 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 agoReply hammer time...

Kaiven myakka2 years agoReply Broke the muffin tin.

bobbuilder093 years agoReply 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

jspencer173 years agoReply 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?

lpdunwell3 years agoReply 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

tincanz3 years agoReply 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 agoReply can you use wood insted of charcoal.

tincanz jbend3 years agoReply 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 agoReply How many nutcrackers do you have??

Lambskin3 years agoReply Can you melt copper with it?

g.petinati4 years agoReply 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.

undinstructable4 years agoReply 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) undinstructable4 years agoReply 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 ;-)

didgitalpunk4 years agoReply 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) didgitalpunk4 years agoReply 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 :-)

didgitalpunk NutandBolt4 years agoReply 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!

didgitalpunk didgitalpunk4 years agoReply 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!

Jimmy Proton4 years agoReply i made one similar to this it it gor hot enough to melt salt and glass and even small amounts of steel

abraxsis4 years agoReply 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.

Chainfire4 years agoReply what were the dimensions,and how refractory did you use?

snowluck23454 years agoReply 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 agoReply 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.

Fred82664 NutandBolt4 years agoReply Try clay and Iron Oxide mix bake it with a small fire before using the blower and try a melt

magickaldan NutandBolt4 years agoReply 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 agoReply 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 agoReply 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)?

Fred82664 NutandBolt4 years agoReply 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.

joel383 NutandBolt4 years agoReply 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 agoReply this is a good way to melt down a lot of beer and pop cans or hard drive bodies and platers

coppeis4 years agoReply Yes but what else can you make with aluminum?

NutandBolt (author) coppeis4 years agoReply 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 1-40 of 57

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