The Fat-Boy Wood/Charcoal Melt Furnace
the seed of obsession...
(originally posted winter
2000/2001)
These
are the parts
I started with, the propane tank is a last minute substitution I made after
considering a bucket furnace with a clay pot liner.
Used propane
tank, a length of pipe pulled from the scrap heap at work, half of a 24"
jack-post, a bag of refractory castable.
The heart of the Fat-Boy is the Refractory Concrete rated to 1650
degree's Celsius or 3000 degrees Fahrenheit.
This requires no additional sand, and has very specific
mixing instructions, listing the max amount of water to be added and the
expected consistency.
Pouring in Water for Safety sake, there is still a strong odour
of Propane.
I had read that propane under pressure can penetrate the
steel of the tank. Another web site detailed an incident where a tank let loose
when attempting a cut with a torch.
I used 2 litres of the hottest water I could handle in
plastic bottle. My theory was that a high moisture content inside the tank would
aid in acting as a spark arrest.
The first cut into the tank was the most nerve racking part
of this project as I had no idea of what to expect.
I think we've all heard of the Darwin Awards, where
individuals are nominated for their unique methods of removing themselves from
the Gene Pool.
I could see far enough into this project that when this unit
gets fired-up, I would need a way to open the furnace to extract the crucible.
The nuts welded to the lid are for steel cable which feeds
through a pulley to a small winch for raising it.
The Crucible is a 3/16ths tube welded to a chunk of 1/4"
plate. The bolts welded to the top sides are great for lifting and the nut on
the bottom is used to aid in pouring.
The weld is very crude, but holds water in a fashion. When
filled with boiling water in a couple of minutes the weld is damp though not
beading with water.
During the test melt with aluminum at extreme temp (glowing a
soft orange) it held up perfectly.
Rather
than drill a series of tedious 1/8" holes to make the intake I opted to cut
so that I could bend the edges inward and add a marginal amount of structural
strength as the refractory is semi fragile.
This has worked reasonably well as the angle of the pipe has
changed a number of times and had to be removed twice since laying in the
concrete.
Among
the many cautions that typify this type of project this info came straight from
the side of the bag.
NOTE: this is a known carcinogen and demands respect!
Always use a working
breather, Safety glasses, and heavy gloves when mixing.
If it wasn't 15 below zero I would definitely have done this
outside. It was hard to mix without raising a lot of dust as the water was being
added
I
used a 10 gallon bucket and mixed about a quarter of the bag at a time. The
instructions suggested that no more than 2.5 litres of water be added to attain
a consistency that holds together just past the point at which it crumbles or
clumps. (as your mixing the description does make sense)
Both
the lid and base have 2 inch spacers set in place to keep the exhaust holes
open.
The lid has numerous screws drilled in with a web of wire
strung through to act as a method of retaining the refractory in place as heat
expands the metal.
The Base also has screws in place, though it is not intended
to ever be turned upside down.
Both the Lid and Base are filled with forms in place, left to cure
over night. If the form for the lid was just an inch larger in diameter there
would have been exactly the right amount of refractory in one bag to fill a
propane tank.
The refractory was left to set-up over night before the forms
were removed and left to cure for a week. Both forms have a slight taper and
were removed without ant damage to the refractory.
The fire-up procedure
on the bag states to raise the temp in 75 degree increments every 30 minutes per
inch of refractory thickness. This was given that only 24 has elapsed since
mixing. As this had sat for a week, it was fired up for a burn without incident.
This motor is from a GE Vacuum cleaner that my dad had in his
work shop in the early 70's. I've had it a number of years but couldn't get the
bags for it but it was working great otherwise.
All surfaces have been caulked with silicon sealant. By
sealing the sand bucket, er... I mean blower chamber from the inside I'm hoping
that the positive pressure aid in keeping a good seal.
Here's the completed blower assembly. This unit looks crude but
works great, and makes a nerve piecing howling sound. Parts List, scrape
plywood, Old Vacuum Motor, kids sand bucket, Kitchen sink drain pipe, misc
electrical switch and cord... cost, zip!
The bucket has developed a small crack and is leaking air
after the first run. Once it breaks beyond repair I'll make a much smaller
version out of fiberglass.
With a good image editor package you might be able to see that this is a
decommissioned analog phone rack. It has sat in my barn for about a year, since
being saved from the scrap heap.
I knew it would come in handy one day...
...today!
After 3 hours of striping card cages and removing numerous
ground straps and cable harness (this unit could handle 150 extensions so had 6
25pair trunks stuffed inside.)
The blower is mounted and there is an exhaust vent cut through
the top. The lid of the Fat boy is raised by a mini-winch with steel cable and a
pulley.
To say that I'm pleased with the "Fat-Boy's"
performance on it's first run would be an understatement.
It took under 15 minutes to melt down 2 1/2 hard disks to the
lumpy mass pictured here.
The burn took 3 charges of wood which were consumed in just
under 5 minutes per charge. We used dry seasoned maple. The first charge took a
while to ignite, ultimately we resorted to diesel, and were off and running. The
howl of the blower now has a more bass type rumble when the fire is roaring
inside the furnace.
A
week has gone by and I would like to make something slightly more useful than a
tin of metal half burnt through the bottom.
My helper and I quickly slap together a quick box to fill
with sand. I won't drag you through the numerous pictures of making the box. Of
note though would be, all joints including the bottom were dado'd with a router
as the sand is fine and will be perpetually seeping out each time the box ix
moved.
I
did throw on a quick coat of sealer because it was handy, as well as some misc
hardware, handles, steel corner protectors.
Rather than wait for the ground to thaw I bought a bag of
sand (washed play sand). The sand was soaked as it was stored outside and had a
number of small holes in the vinyl sack.
I ultimately ended up placing a steel bucket with wet sand
into the firebox of our wood furnace. This is serious stuff especially around
children as when it is brought out of the fire (with heavy gloves) it doesn't
look hot.
By constantly pouring between two buckets with about a
quarter bucket of cool wet sand mixed it took about 10 - 15 minutes of slogging
before I felt comfortable leaving it unattended. Adults and children alike
simply can't resist running their hands through sand.
This is
a rather large dice I cast just to play with foam cutting and the "Lost
Foam Casting" method. The key lessons learned were to wait at least
10 to 15 minutes for the metal to solidify. I broke the sprue off by lifting it
and there are a number of gouges where I was poking the iron into the sand. This
was immediately after the pour.
Secondly pour quickly but carefully into the well formed
funnel leading to the sprue which is level with sand. If you pour too slowly the
first trickle of molten metal will evaporate the form, and the sand will start
to collapse into the form before more metal can fill the cavity.
The same thing would happen if there is too little molten
metal to fill the form, since the sprue will be part of the next melt there
really is no waste.
I had
to wait until dusk to capture the best picture that I could and still feel safe
working around the hot metal. The flames shoot a good 6 inches out the top and
around the sides.
This the reason that I live on the end of a dead end side road.
The noise and smoke would probably cause a strain with neighbours. My wife has
been just excellent, initially I had it just out side the garage door, even I
thought this may be a bit to close. The Steel cable and clamps are holding up
nicely as they are slightly off center of the top flame.
This should give you sense of just how hot this gets. I had Sandy snap the
pictures directly on the computer, as I lifted the lid.
All images on this web site are either stripped from Video
tape or live video via a Panasonic S-VHS Video Camera via ATI All-In-Wonder-Pro
capture card. I moved the camera outside and ran a 50ft video line back to the
shop system.
In
the time that it took me to walk around to the front and clamp on to the
crucible it becomes noticeable that things are cooling down.
I welded a pair of huge flat washers onto the ends of a set
of tongs, and have a fire poker that I hook into nut welded on base of the
crucible.
This is the 4th pour and the crucible is holding up very
well.
Foam
pulley forms...
...First look at poured pulley
Straight
out of the sand...
...Semi polished (first real part)