Zero Cost Aluminum Furnace (No Propane, No Glue / Epoxy, No Welding, Individually Replaceable Parts)




As seen from the picture and title this instructable is about how to make a zero cost aluminum furnace from salvaged items from your local scrapyard or around the house.

Please be advised that though this aluminum furnace can truly be made at zero cost, for some steps you may want to substitute a tiny bit of money for less hassle and trouble, throughout this instructable i shall be pointing out these steps and how you could do so.

BTW this aluminum furnace build can seriously smelt down a lot of aluminum, but takes a while to heat up, so ensure that you have a large store of scrap aluminum before using, for maximum efficiency.


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Step 1: Materials

If you're reading this step then i guess you're interested in building a Zero Cost  of your own, if so, go salvage / hunt for the following materials

1. Small stainless steel or steel pot, preferably without handles X1
(i found mine under the kitchen sink, by the looks of things it has been there a while)

2. Cement powder X min 1kg
(i got mine by sweeping up left over cement powder at a construction site after they had finished)

3. Milo tin / milk tin / circular biscuit tin , doesn't need to be empty X1
(i like drinking milo, so i already had one to begin with)

4. Very old but still working oven / toaster with heating elements that aren't in a glass cylinder X1
(i got mine when my mom had to get a new oven to prepare Christmas dinner)

5. Misc lengths of wire and both electrical and hardware connectors

6. Cardboard X1sheet

7. Small stainless steel or steel bowl X1
(kitchen stock)

8. Small ceramic plate or tile X1
(kitchen stock)

9. Scrap aluminum in the form of drink cans or otherwise
(beer cans ^_^)

Step 2: Furnace Casting + Coil Bending

This step deals with Furnace Casting and Coil Bending of the aluminum furnace.

Furnace Casting
1. Take 1/4 of the cement powder you have (250g min) and mix it well with water
2. Pour it into the steel pot and let it set and harden into a level concrete surface
3. Make a cylinder that snugly fits around the milo tin using the sheet of cardboard and some tape
4. Center the cardboard cylinder in the pot, on top of the layer of hardened concrete, and place the milo tin in it, add some weights onto the milo tin just to stablise everything.
5. Take 3/4 of the cement powder you have (meaning the rest of it) and mix it well with water
6. Pour it into the steel pot around the cardboard cylinder and let it set and harden into a concrete ring
7. Remove the milo tin by sliding it out of the cardboard cylinder, then peel out the cardboard, if any cardboard residue remains, burn it off with a flame.

Coil Bending
1. Take apart the oven and remove the longest heating element available
2. Un-coil the heating element and proceed to re-coil it into concentric circles, as seen in the picture, at the bottom do a S-shape so as to give the bowl that is going to rest inside some support
3. Ensure that the individual coils don't touch each other or the pot for that matter, then place it into the concrete ring you've just made.

Step 3: Electrical Wiring

This step deals with the electrical wiring of the aluminum furnace

Electrical Wiring
1. The heating element is no more than just a gigantic resistor, so all we have to do to is hook it up to mains voltage, and it will start to heat-up, eventually reaching aluminum melting temperature.
2. The problem lies with the nature of resistors, as they heat up their resistance decreases, thus allowing more current through them, which causes them to heat up further. This positive feedback loop can be devastating if left unregulated, as the metals in this furnace melt in the following order
aluminum scrap @ 661 °C
steel bowl and pot @ 1538 °C
heating element coil @ 2852 °C
after which the circuit would be broken thus breaking the feedback loop.
3. To solve this problem, i highly recommend having a thermocouple temperature meter, and if the temperature exceeds 800-1000 °C, cut the mains power until it cools down some or use a light dimmer circuit to regulate how much power gets into the heating element coil, thus slowing the heating process so much and so accurately to the point where heat production = heat desipitation, thus there would be no nett increase in temperature over any substantial length of time.

Step 4: Bowl + Lid + Replacing Parts

Other misc stuffs

As with any furnace a crucible is needed, however since we are only melting aluminum, a steel bowl can be used instead, because steel has a much higher melting point than aluminum, it is also much easier to obtain as compared to ceramic crucibles

In the event that by some chance your heating element coil used in this furnace refuses to produce enough heat to melt even the smallest batch of aluminum, a ceramic plate or tile can be used as a lid and insulator to trap the heat generated in. This method can also be used to speed up the heating of large batches of aluminum or the initial start-up time required.

Replacing Parts
After prolonged use the constant heat could cause wear and tear in all parts of the furnace, by making parts that fit together instead of casting it as a whole, individual parts can be replaced without discarding the whole furnace. The most likely scenario for this would be the positive feedback loop problem described in "electrical wiring", gone wrong.

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    49 Discussions


    2 years ago

    Have you actually used this thing? Did it melt yoiur aluminium? Pics?


    2 years ago

    Can you really bend a long, straight heating element like that without wrecking the inside? Sounds brilliant, but too good to be true.


    3 years ago

    PS: Resistors have a POSITIVE temperature Coefficient; meaning that the hotter it gets, the more resistance it has. Resistors, and ALL conductors have this 1/1 Proportional temp/ohm ratio. Semiconductors, like Silicon, Germanium, (Used in transistors and Diodes,) Have a NEGATIVE temperature coefficeint; meaning that the hotter it gets, the lower the resistance. That's called a cascade, or Avalanche.

    Dimmer switches don't work as well at higher wattage, they lower the current in the coil by increasing resistance in the circuit. This resistance creates a second point in the circuit where energy needs to be dissipated in the form of heat, where you would need a big heat sink. What you need is one of the thermostats from your stove. They work on a different principle.


    Reply 3 years ago on Introduction

    This is not true. Dimmer switches are rheostats and they are triac devices that turn the AC voltage on after a certain portion of the 1/60th second cycle time of AC voltage. Then they shut off again when the voltage crosses 0.

    Only very ancient dimmer switches would work by load-balancing the way you described. Maybe for old theater equipment and the like. I'm not totally familiar.


    Reply 3 years ago on Introduction

    First rule of correcting should be to make sure you're correct. I am however wrong to call them "rheostats." Rheostats are usually used in the circuitry but the typical dimmer switches are actually called triac-dimmers, I believe.
    So urhm take what I said with some measure of caution. Not a part of electronics I'm totally familiar. Also, now and days there are different dimmers besides triacs because triacs do not neccesarily work well with flourescents of LEDs.

    bi-metalic strip that bends when heated and open the electric circuit they form ... after cooling they regain its original form and stablish the circuit again... on-off-on-off..............

    but there are other methods!


    Reply 3 years ago on Introduction

    Hi piedade. Such metallic switches may have been used in ovens many years back, but they have tremendous hysterisis and no doubt they are not used anymore. I only see them for saftey failure switches. Maybe some thermostats for old rooms, as well, have them.

    yes, you can use an electronic dimmer (those used to dim incadescent light bulbs). Just check the dimmer specifications to see if it can handle the amount of power needed for these oven heating elements.


    5 years ago on Introduction

    What are you running your element from, household ect. I Am in the process of making this and currently I have my doubts as to the validity of this instructables alleged results


    9 years ago on Introduction

    Have  you actually used this?  It does not seem to me that the heating element would get hot enough or that that lid would hold up very well.  It is also dangerous to use concrete as it is prone to forming air bubbles and exploding.

    4 replies

    I have used this set-up to melt beer and soft drink cans before, and with satisfactory effect, however i must admit that i swapped out a new stainless steel bowl as the old one was badly stained and didn't photography well, the pot however remains badly oxidized. The heating element was taken from a 1000W oven thus has enough juice at least for aluminum especially with concrete and ceramic as the insulators, also the concrete i used doesn't seem to have any problems with the heat, as i have thoroughly bone dried it.

    The exploding concrete you mentioned may have been caused by improper drying of the concrete, this residual moisture would form steam at high temperatures and provide the pressure for the explosion, this may also occur in plaster of paris.


    Reply 9 years ago on Introduction

     If too much water was mixed with the concrete to start with, water droplets can remain inside, causing an explosion when the water forms steam.  I would consider a lid and safety glasses mandatory, though, just because of this risk.  It is not worth losing an eye just because you were counting on your mixture to be perfect.

    Industrial furnaces of certain types use specialty concretes/mortars for their furnaces, so this isn't a bad idea in general.  Concrete depends on the chemical bonds formed with the water and mineral constituents for strength however, so I would be interested to know how the construction concrete is holding up after heavy or long-term use.  I would be surprised if it didn't slowly crumble as the water is driven off, but it was free, so perhaps that is acceptable wear-and-tear.

    Overall, it was a clever use of materials and a simple design for this project.  Good job!


    Reply 9 years ago on Introduction

    1st up, thanks for the compliment, and now that you mentioned it, the upper layers of the concrete seem to be ever so slightly flaking like a pastry then very slowly being burnt away by the heat over time, however the process is so pitifully slow that by my calculations, it should last the better part of a year at least, even with daily use.


    i would assume that the slow heating of the element, and the porous nature of concrete would allow concrete to be relatively safe. if you're really worried, a similarly cheap method could be a terracotta flower pot... don't pour water, or molten metal on the concrete/terracotta and you should be fine. good job.


    9 years ago on Introduction

    Interesting instructable.

    • Any safety measures? safety glasses, protective gloves, etc... May I suggest that you add a word about that.
    • Do you melt aluminium just for the fun, or is it part of another project?