Jane, There are two answers. Casters doing large amounts, and needing
to control burnout fumes, can use steam dewaxing to melt out most of
the wax prior to burning out the flask. The steam will melt normal
injection waxes, but is not effective for most of the carving waxes.
With steam dewaxing, the majority of the wax is removed before the
flasks even go in the burnout kiln.
Once the flasks are in the kiln, though, you leave them there. “even
when it’s 1350 degrees” suggests you may not have realized that by
the time the kiln reaches that temperature, there’s no trace of wax
left. It’s gone. At that point, you’re simply burning off residual
carbon in the molds. The injection waxes themselves generally melt
around 170 degrees F, carving waxes are in the mid 200s. You could,
if you wished, place the flasks on some sort of tray for that initial
heating stage, and remove the tray after a suitable amount of time,
along with the wax that has by then run out of the molds (you put
them in the kilns sprue hole down for just this reason) There’s no
point where the molds would ever be full of wax melted enough for you
to pour out, since as it melts, it flows out on it’s own already.
Most small volumn casters don’t bother to worry much about the wax
that flows out into the kiln. It burns off just fine.
As to carbon, one of the key differences that may exist between
kilns intended for wax burnout, and those used for other things like
enamels, is that burnout kilns need sufficient air flow to keep a
supply of oxygen in the kiln. If the kiln is designed right, then the
atmosphere in the kiln will remain oxidizing throughout the burnout,
thus eliminating any carbon that exists as a residue from the wax.
The reason for holding the 1350 temp for more than a brief time is
that some of the carbon will be imbedded in the investment from when
melted wax was absorbed by the investment, and this carbon takes a
bit longer to fully burn away. That within the main kiln chamber is
gone before you even got to 1350, and in a properly designed burnout
kiln, the carbon does no damage to the kiln. Eventually, the heating
elements burn out, but that’s due to oxygen and general degredation
of the element just from heat, not because of the carbon from