I’ve got a large Sierra kiln for doing burnouts. It holds sixteen 2
1/2" diameter flasks.
My standard casting procedure is to invest the flasks, let them sit
for 2 1/2 to 3 hours, prepare them and start the burnout.
I let it sit at 250 degrees for 2 1/2 hours (to dry out the flasks),
then ramp up to 700 for 2 hours, then up to 1300 for a while and back
to 1000 to cast. I normally start burnouts late at night, and cast
the next day.
This past Saturday I started a burnout in the middle of the
afternoon, and left for a while. When I returned to the shop during
the 700 degree phase of the burnout. I found water dripping down the
front of the kiln below the door. It was running onto the digital
control panel. The display was going nuts–it was displaying random
shapes instead of time and temp like it normally does.
The burnout continued to proceed, and by the time it was ready to
cast, the display was back to normal. This can’t be good for the
kiln…
I’m assuming the water is coming from the moisture in the flasks, as
I see no other place else from which it could have originated.
Obviously the 2 hours at 250F isn’t drying them out.
What can I do differently to prevent this from continuing to happen?
And is it safe to put a line of silicone sealer above the top of the
digital control panel to keep moisture out of it? The front of the
kiln gets warm during burnouts, but not too hot to touch.
I suspect you need more ventilation (keeping the door open wider the
first few hours works fine) to allow steam to escape… or open the
plugs if you had not. I keep the door ajar about a third the first
couple of hours, especially with a full load. And it also could be
other variables such as investment too wet this time round.
I would let the flasks sit longer until fully dry or at least nearly
dry. Iknow that some like to start the burnout cycle while the
moisture content is still relatively high to, in effect, steam out
the wax. I always let the flasks sit for at least 4 hours, usually
longer. I know the the investment manufacturers usually want you to
let the flask sit undisturbed for a certain length of time (usually 3
hours I think) so that the investment can build up green strength,
that means the investment can take a shock better, thermal or
otherwise if it’s allowed to sit.
If I were you I would definitely wait longer before starting your
burnout, nobody likes a drippy kiln.
It does depend on what was you are using as to how soon you put the
crucibles into the kiln. We often cast Filo wax, a wax that is not
supposed to be good for investment casting (it is hard, requires a
high temp before getting liquidus, and expands when heated) but if
the flask is “burned out” while rather new or wet, the steam does a
great job at steaming out the wax and the castings come out
great… Just a thought…
It probably is important to find out why water is leaking out the
front, but I can see why sealing the top of the control panel would
also be a priority.
I don’t know how suitable it is for sealing out water, but I
recently bought a “High Temperature” sealant (I think it was silicon)
at my local Ace Hardware. I bought it to seal the flue above my water
heater.