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NOTE: THIS ITEM CAN BE USED TO MAKE CASTINGS AS GIFTS FOR ANY HOLIDAY OR OCCASION!
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.
Step 1: 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
8. Small ceramic plate or tile X1
9. Scrap aluminum in the form of drink cans or otherwise
(beer cans ^_^)
Step 2: Furnace Casting + Coil Bending
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.
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
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
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.
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.