Chances are you’ve thrown these things in
the trash without even knowing it. But if you use them like this, they’ll spawn an
electric arc hot enough to melt any metal known to man, and even turn rocks into lava.
In this project we’re modifying a fire brick and some flashlight batteries, to build an
electrical arc furnace, on a budget. Let’s start this project, with a heavy duty
lantern battery, and this alumina silicate refractory brick. The brick is 3” tall,
4.5” wide, and 9” long. Let’s get to work making the furnace by measuring lengthwise, and marking
at 3”, 4.5”, and 6”. This is where it needs to be cut, so it’s a good idea to
draw perpendicular lines with something like a combination square to make it as accurate
as possible. Now get a mask ready, because, according to the safety sheet, silica dust
is something you really don’t want getting into your lungs. These refractory bricks are
extremely lightweight and full of air bubbles, which is why they’re so great at insulating
heat, but it also means we won’t need any fancy tools to cut them. A simple wood saw
is all you need because the bricks are so soft. In reality, you could probably carve
them out with kitchen utensils, if you really needed to. I put a couple of bricks under
the edges to help channel the dust, and prevent the blade from scratching the table when it
cut through. Ok, the 3 lines are cut, and you can see they separate the brick into 4
pieces. I designed it this way so that one fire brick will make two furnaces, effectively
cutting the cost in half as well. Let’s move on to carving out the reaction chamber,
and giving the furnace some special features. I’m using a 3/8” drill bit and a 2”
Forstner bit I got at my local hardware store. The Forstner bit makes it easy to target the
exact center of the brick, and doesn’t take much of an effort to begin chewing away at
the refractory material. Drilling too fast could rip the brick apart, so let’s take
it slow and steady until the hole’s around 2” deep, which should leave a 1” base
of insulation at the bottom. Clean out the dust, and you’ll see we’ve got a nice
little chamber for our reactions to take place. Now let’s turn the brick on it’s side
and use a 3/8” drill bit to burrow down near the top. When it penetrates into the
chamber, keep going straight down into the other side. And when it pops out the bottom,
gently push the bit outward to break through the wall, exposing the holes. Let’s do the
same thing with the front end of the furnace, except this time we’re not going to go through
the other side. We’ll need to modify this hole by drilling inward at about a 45º angle
until the tip of the bit meets the bottom of the chamber. If we carefully work the bit
upward until it breaks loose, and clean up the edges a bit, the bottom half of the furnace
is finished and looks awesome. The holes on the sides are for the electrodes, and this
last one has a dual purpose. For watching the reaction, and pouring molten metals. Now
the two smaller pieces are the lids for the furnace, and should only need a very small
modification. Two 3/8” holes drilled 1” from the ends, and 3/4” from the sides to
form a place where we can safely store the electrodes when they’re glowing orange,
and too hot to put anywhere else. Speaking of electrodes, we’re going to need carbon
rods like these to strike the arc, because they’re the only things that will handle
the extreme temperatures. I went to a local super center and picked up a 2 pack of 6 volt
lantern batteries for under $5. These ones are the “Heavy Duty” kind. And don’t
worry if they’re new or used, because completely dead batteries will work just as well. Now
we need to crack open the container and my tool of choice for doing that is a pair of
wire cutters. If we break the lid off the top and cut the two wires holding it on, we’ve
got easy access to the 4 battery cells inside. Go ahead and snip the wires connecting the
cells together, then pinch the caps in the center, and gently pry them upward. With
a little bit of effort they should pop right out of the casing, and just like that you’ve
got a carbon electrode ready to go. But that’s not all. These batteries have all kinds of
fun things hiding inside. The casings on these cells are made of zinc, and they’re packed
with manganese dioxide. So use something like a screwdriver to scrape around the inside,
pulling all that crumbly gunk out. The manganese dioxide could be saved for other
experiments, but in this project we’re just interested in the carbon rods, and the zinc
casings. And I’m really excited because we just scavenged 8 of them. Now just for fun, I wedged the zinc battery casings in my bench vise, and started cranking to see if it would
make the casings a bit smaller. Apparently you can crush them down so they’re really
compact, and that’s great because we need them small for an experiment we’re going
to try in just a minute. The last thing we need to make for the mini arc furnace is a
pair of adjustable stinger grips. I made a trip to the hardware store for two 5’ lengths
of 8 gauge stranded copper wire, two 1/2” copper couplings, #20 stainless steel hose
clamps and two sets of 6” locking pliers. I modified the pliers by removing the rubber
handle grips to expose the metal, then stripped the end of the cables to expose the copper,
so they could be secured directly to the pliers with the hose clamps. Now, if you put the
copper couplings on the other ends of the cables, and hammer them flat or clamp them with a bench vise, they make little copper lugs you can hook up to an arc welder for power.
Like this homemade version I put together with microwave parts. You might remember that
project where we center tapped the two transformers so it could power the arc furnace on 120 vAC.
However it works much better on 240 volts, so let’s just leave it as is. Now since
the electrode grips are adjustable, they can be set to bite perfectly onto any size carbon
rod we need, and hold them firmly in place. But there is something you need to know about
these scavenged rods before you use them. The first time they make electrical contact,
they’re going to catch on fire. There’s some kind of wax in the rods that bursts into
flames as soon as they touch, and it’ll take anywhere from 20-30 seconds to burn it
all out. It generates a lot of heat and a lot of smoke, so try to do it outside and
away from anything flammable. At this point our mini arc furnace is completely ready for
operation, so let’s test it out, with the zinc battery casings we scavenged earlier.
With one casing in the chamber let’s go ahead and set the lid in place, then power
up the arc welder so the electrodes are charged and ready for action. The magic happens when
the rods are pushed through the holes in the sides, and suddenly bump into each other,
striking a dangerous and blindingly hot arc of electricity. In less than 10 seconds, you
can see the rods are already blazing hot, and amazingly, the metal has already liquified. 8 casings
later the chamber is full of liquid zinc. So now that it’s runny, let’s test out
the functionality of our built in pour spout. This is how easy it is to transfer molten
metal from the mini arc furnace, into makeshift ingot molds. Now zinc has a relatively low
melting point, but this furnace is resilient enough to tackle high temperature metals like
copper, and even steel as well. So if you’re in the mood to see glowing streams of molten
copper, or sparks flying around the room, look for those extreme experiments in another
project video. Alright, our zinc muffin has hardened, so let’s knock it out of the muffin
tray with a screwdriver, then dip it into a bowl of water to quickly cool it the rest
of the way. The result is a beautiful chunk of solid zinc, to add to our homemade metal
collection. As a word of caution, in you breathe any of the zinc oxide fumes when melting zinc,
there’s a small chance of catching metal fume fever. So if you recycling zinc yourself, be sure to wear a respirator, or do your experiments outside to reduce the risk. Well
now you know how to extract carbon electrodes from old flashlight batteries, and carve insulating
fire bricks into custom arc reaction chambers. By the way, if you cut the brick into 3”
blocks, you’ll get 3 furnaces. And you can even modify them to hold graphite crucibles
for smaller experiments. Well that’s it for now. If you liked this project, perhaps
you’ll like some of my others. Check them out at www.thekingofrandom.com
Thank you! :)
I want to try this.. but I don't have a power supply :(
to do list