first
off, a group shot of all of the wax skulls on their wax tree. the bright
red thin wax lines are all vents, which will eventually allow air to
escape so that the entire shifter knob will fill out. these things require
alot of venting, as you can see, and each one is attached by
melting/welding it to the piece and another vent going up to the top of
the cup.
i think everybody's knobs oughta be visible in this one, with 16 of the 32
pilots i am casting this go around in the front, followed by firemen, more
pilots, and some others in the back. up until this point is what took so
damned long, as there was alot of work in getting the few imperfections
incurred in wax casting fixed and ready for this stage. doing 97 knobs and
some other things, and it really filled up my time.
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after
all of the waxes are "chased (what we call the clean up work),"
"sprued (attached to the 'tree' for dipping)" and vented, i then
start the ceramic shell process. each piece will be dipped in a ceramic
slurry up to 9 times. the first two coats involve a thicker solution with
very fine particles, onto which very fine sand is sifted for body and
strength in the ceramic. the next two coats use a slightly coarser sand,
and the remaining coats use coarser yet sand and a runnier slurry with
less fine particles in it. the final coat is a "sealer" and
eliminated the sand application to seal in the layers and sand so that it
cannot be rubbed off.
in this picture, the trees of shifters are visible with just the first
coat on them. in the lower right corner is a small shot of the slurry
tank, which must always spin to keep the particles agitated. sitting still
for only 5 minuts can cause the particles to settle, which can bury the
agitator paddle. the bottom literally starts to rise as this happens. if
there is a power outage, it takes 24 hours to chop up this settling AFTER
we pry the agitator paddle out of each tank. that's a pretty rough task in
itself.
just before i came in tonight i finished the second coat and should finish
up the ceramic shells by sunday or monday. my next post will talk about
melting the wax out of the shells, and then casting after that.
one last note, you might notice how yellow-green the tank is, and how
the trees of skull sare a little orange. we use a dye additive that is
orange in the absence of water and yellow-green when in the presence of
it. one of the ingredients in the slurry is distilled water, and this
allows us to be certain that shells are dry. when my dad first started
casting bronze, we hadn't discovered this, and the shells were snow
white when they were sopping wet and bone dry... makes it alot easier to
get it right, because repeated wet coats cause weak shells. with bronze,
there is much more pressure than aluminum, and blow-outs are more likely
if a weak spot in the shell exists. the bronze is poured at over 2000
degrees, 300 lbs. at a time. that amount of metal at that temperature
can be interesting, i'll save those stories for another time.
also note that everything, the sprues, vents, and skulls are being
covered with ceramic, and this shell will grow with each dip until it is
about 1/4" -3/8" thick...
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| here's
the next step of the process. in the lower right you can see the shells
with wax still inside them, ceramic dipping recently completed. i've made
sure the tops of the cups have been cut off to allow wax to drip out, and
drilled a few vent holes in the main sprues so ease these things as the
wax melts. the main picture is of the loaded kiln, wax dripping and
burning out of the shells. this kiln is a large stainless chamber with a
propane burner and reaches 1500+ degree f. a hydraulic ram from an old
garage lifts the rack of shells into the kiln where it is held by a pair
of levers and the ram retracted. wax runs out the grating that makes the
floor of the rack. after the wax stops, about an hour later i pulled the
shells, slightly glowing from heat, out of the kiln and rolled them to a
safe spot to cool. the white shells in the lower right are the freshly
burned-out shells, now ceramic molds.
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alrighty!
so i poured around 100 lbs. of #356 aluminum today, and here's how it
went. first off, there's a large picture of my pouring rig. the two sets
of tongs, one for lifting, one for pouring, were made by my dad when he
first started casting bronze. they've upgraded to a 300 lb. crucible and
an overhead hoist to pour with, so when i set out to build a casting
setup, these were just about right. the inset picture is FLAME ON in my
little furnace. i built this thing myself a little over a year ago, if
memory serves. the blower and burner behind the furnace is a pretty
antique item. reconditioned and refreshed when they started pouring bronze
and like the tongs, not big enough anymore. the burner pipe i rigged up
myself from the design used by my father. we use propane gas and this
little refractory blanketing furnace gets the job done pretty damned
quick. |