Before
you begin it is important you understand the elements you will be
working with. At times you will have uncovered liquid metal
at several thousand degrees. At other times you will be
igniting vaporized motor oil. Poisonous vapors, burn and
explosion risks all come with this project. Understand the
fundamentals before you attempt this construction on your own.
This guide is intended as a walk through on how to implement
processes you should already understand before beginning.
The
energy for this foundry comes from waste oil. Waste oil can
come from several sources. The most common are used cooking
oil or used motor oil. When hot enough both of these oils can
burn very clean producing huge amounts of energy. In fact oil
can have over 150,000 BTUs per gallon. What this design does
is burns super heated oil in the presence of large volumes of air.
A typical amount of air is 150+ CFM. Thats more air
than what a mid-sized car moves at 3000RPM. Once the oil is
burned the exhaust gases are exhausted into the furnace body which
houses the crucible. These gases are what provide the heat to
melt the metal.
Start
with two 12" sonotunes one cut to 17" tall and the other cut to 14".
Cut a 10" wide section out of the entire length of the
shorter tube and a 10" wide, 14" tall section out of the bottom of the
taller tube. Now using tape secure the two tubes together as
shown above. Because of the weight the refractory will exert
on the walls of the tubes, reinforcement is needed. A simple
fiberglass patch will do the trick or in a pinch lots of tape.
The
inside walls of the furnace and burner box are constructed in much the
same way. For the furnace cut a 15" piece off the 8" diameter
sanotube. For the burner box a tall plastic coffee can is
perfect. To make the connections between them you will use 1"
sections of wood. Make sure the holes in the tube and coffee
can fit tight around the wood plugs or refractory will be introduced to
the furnace/burner cavity.
Now you
need to fabricate the system that will inject the oil and air into the
burner. For this tap a 3/8s compression into a 2.5" cast iron
pipe at a 45 degree angle. Then run at least 15" of
3/8s copper pipe back to a needle valve. This is the valve
that will control your oil flow.
With
everything cut and fabricated you are almost ready to start.
Before you do though, double check the fit of all the
components and make sure all the steps are clear in your mind.
From this point make sure you have at least 3 hours to
spend. For a project this size you will need the following on
hand.
50 Pounds of sand
50 Pounds of fire clay
50 Pounds of Portland Type II cement
20 Pounds of perlite.
Start
building your refractory base by mixing 1.5 parts of sand with 1.5
parts
cement and 1.5 parts of perlite. All the ratios given here
are done by volume not weight. When mixing try to target a
consistency close to cream cheese. While this is a little
loose, it will aid in the addition of the fireclay. Once you
are happy with the mix add 2 parts fire clay as you continue to mix the
refractory. More water will be needed but try not to let the
mix become loose. The end goal is a mixture that is like
bread dough. When your refractory looks like the picture
below you know it is happy.
I opted
to build my furnace on a cart to make moving it easier.
Unless it has a permanent home I suggest the use of a cart or
large wagon. If you do use a wagon or cart it is a good idea
to lay down a thin insulation layer. I just used a piece of
fiber glass I had laying around. This step is not needed but
it does provide peace of mind. With just the outer tube in
place, start by building up a 2" thick layer of refractory on the
entire bottom. Take care to avoid creating air pockets.
Once you have the 2"' base layer, position the two inner
tunes and their connection blocks as shown below. In the
furnace body, I made a small platform to hold the crucible.
The platform is an optional step but it does make life easier later
one. Because the refractory is unbelievably sticky, you can
freehand pretty much any shape you want. Just remember as you
fill the mold to watch for air pockets. With the refractory
added
up to the top of the coffee can, cut a hole in it just large
enough
for the 2.5" T. Place the cast T in place and aim it for
toward
wood connecting blocks.
Assure no
refractory ends up on the threads of either the oil
compression fitting or the cap side of the T. At this point
you are
done for a few days with the furnace body itself.
As the
refractory cures it will get hot and start to dry. To combat
cracking you should keep it covered with plastic for at least two days.
Also for the first 24 hours you should mist it with water
often.
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