My guess it the heating coil burned up. Coils can be replaced
although it is not a simple job. If you try to repair the oven check
out your local jewelry supplier for a replacement coil. Local
ceramic shop stock kiln heating coil that will work. be sure you get
coil for the voltage you will use.
The connection of the coil to the control wires is most critical.
Ceramic shops sell screw clamps that work well. The joint must be
tight in a fixture that will not heat up and melt. The joint is the
most common place of a failure. If a flask touches a coil you may get
a burned coil. Coils can be burned up if large flasks are placed next
to the coils. The flasks traps heat and will cause the coil to melt.
You will need a bunch of the wires pins that hold the coil to the
fire brick.
I have had heating coils burn up a couple of times during my 30
years of casting. You get a real spasm in your gut when you notice
the temperature is not increasing. Early on I replaced the coil and
started the burn out cycle again. In those few cases the temp in the
oven was around 800 degrees before the coil burned up. I was
fortunate in all cases in that the castings came out OK.
I now have two burn out ovens and rarely fill both at the same time.
The last time a coil burned out I transferred the flasks to a hot
second oven.
The actions to take after the oven fails depends on what is in the
flasks. If the flasks are filled with original work I suggest you
start the burnout cycle on the flasks and hope the castings come out
OK. If you first pour ends up with a failed casting you might not
want to waste metal to cast the rest of the flasks.
If the flasks are filled with reproductions from molds I suggest you
start over.
I hope if you are vacuum casting sterling you are using the anti
fire scale casting process described in Orchids “Tips from the
Jewelers Bench.” If you use the process you will get castings without
fire scale.
Lee Epperson