upon the first firing of the furnace, disaster struck!
My propensity and unswayed determination to use soup
cans as crucibles finally fought back. Not realising
that the crucible had developed a leak during the
melt, I kept adding more and more aluminium thinking....
"wow this crucible can certainly take a lot of
low yield from the subsequent pour hinted that something
was drastically wrong. Next came the stench of burning
PVC. Luckily, I had employed a segment of foam between
the PVC and blower, which acted as a 'fuse' and let
the aluminium spill before entering the blower.
Mr. PVC says
"I give up, you win..."
The foam block
used for the first casting by the new furnace with
the blower pipe, the furnace was fired up for the
second time. I had no ingot moulds at the time, so
decided to do a quick lash up 'lost foam' casting.
Lost foam casting
involves a piece of foam shaped to the desired metal
shape with a sprue attached. The sprue acts as a gateway
for the metal pour. The piece of foam is then stuck
in fine grain sand with only the sprue visible.
the molten aluminium is poured onto the sprue head,
the foam quickly gives way and the liquid immediately
follows before any sand can fill the gap. Once the
mould is full (and all the foam is gone), the metal
solidifies in the shape of the foam, supported in
place by the sand.
sprue is then cut off the casting after it has cooled.
The foam piece
held in place by sand (albeit not fine-grain sand)
casting - not great, but not too bad
Here is the result
of the first attempt at lost foam casting. I had tried
to engrave "Penguin's Lab" into the foam,
but this did not turn out very well.
The cavities in
the casting are due to bits of slag which happened
to find their way into the pouring process. I later
concluded that the aluminium was being poured too
cold, and that the furnace did not meet the temperatures
required to fully melt the aluminium.
fault was identified at the bottom of the furnace.
Where the air distributor contacted the crucible,
the floor of the crucible was being cooled by the
incoming air. The arrangement was such that the two
would be touching, as the soup cans were too high
to allow for any coals inbetween. This was easily
fixed by cutting down the crucible height.
improvement was made through the introduction of a
new blower - this time in the form of a hairdryer.
I removed the heating coil in the dryer, and rewired
it to run on 12VDC - the specs of the motor. This
sucker pushes through so much more air than the last
The new improved
blower system, complete with 240VAC - 12VDC transformer
A few kilos
worth of aluminium scrap! Beautiful.
While the improvements
were being made, I also abused some old circuit boards
I found to scavenge some very nice aluminium boards,
heatsinks, RF shields and chassi.
As most of these
pieces are too large to fit in the crucible, I usually
dump them in the furnace after a casting session,
then perform a crude hammer, fatigue, and rip strategy
when the aluminium is close to its melting temperature.
At this temperature, aluminium is very brittle and
is easily smashed into smaller pieces.
You can easily
tell when the aluminium is getting soft by hitting
it with a hammer. If it still 'rings' like usual,
then its still cold. If it sounds 'dull' and rather
unresponsive, then you know its nice and hot.
is the new furnace arrangement being fired up, and
it sure is firey - the crucible is glowing bright
orange and flames are being sent whipping up through
the vent hole.
crucible glowing orange-hot
of foam ready for casting
Here is a new
foam mould ready to be packed in sand and cast upon!
The new furnace arrangement is a LOT more efficient
than previously, and takes roughly 15 minutes to completely
transform room temperature aluminium into its liquid
I have also found
that there is considerably less slag output and no
aluminium sticks to the bottom of the crucible after
is a crucible load of aluminium being poured into
the foam mould pictured above. When pouring lost foam
castings, it is important to keep pouring when the
foam bursts into flames, as this is when the liquid
must keep up with the rapidly dissappearing foam before
the sand moves at all.
shot is a still capture from a video, since I didn't
want to waste time trying to get the self timer to
go off at the right moment. However, I might have
to do this in the future, as the resolution from these
videos is really quite baaaddddd....
being poured into a foam mould using the lost foam
produced from the furnace
Finally, we have
here two more "acceptable" castings. The
right most one is the result of the pour pictured
above. I tried engraving my surname "Peng"
into the foam at the last minute, but unfortunately
I did not pour the aluminium fast enough for this
mould, as a large chunk of it was consumed by sand.
The sprue hasn't yet been removed, and the casting
is upside down.
The left most
casting is quite a nice one. Although I had no idea
what I was making (only that it was something vaguely
geometrical), the aluminium filled the mould perfectly.
The sprue has been cut off this one. Unfortunately
I haven't found a use for any of these castings yet.
Maybe I should cast something useful in the future...
I try my hand out at greensand casting too- another
casting method which involves a sand and clay mixture
which is shaped into the desired mould. The main advantage
of this method is that you can easily produce multiple
castings, whereas the lost foam process sacrifices a
load of sweat, tears (if badly performed), and of course
foam everytime a casting is performed.
lost foam castings