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Casting misadventure


#1

I ran into a problem Saturday, casting using some new-to-me
equipment. I bought a used Memco Electro-Vac and programmable kiln.
Earlier in the week I tried two small flasks in my old smaller kiln,
just to make sure I could make it work, which it did brilliantly.
Saturday I had six 4 x 6 flasks all hot and ready to cast and the
heating element in the caster burned out after the first flask.

So now there are 5 flasks, that represent a lot of work waxing, and
no chance of repairing the machine until Tuesday. Each casting was
about 300 grams of sterling deox. My question for the casting sages
on the list is what should I have done?

  1. Let the flasks cool and reheat when the machine is fixed.

  2. Keep the flasks at temp for the next 3 or 4 days. What would be a
    good holding temperature?

  3. Melt the metal in an open crucible with a torch and use the
    vacuum chamber on the Elecro-Vac like you would a vacuum table.

I tried the last option. The second flask cast beautifully. Two of
the other four were probably not hot enough because the metal did not
flow into many of the smaller cross sections. I saved about 50% of
my work. Using my trusty centrifigal force caster I usually only melt
about 150 grams at a time, so my judgment for the bigger casting
under the torch was not so good.

Stephen Walker


#2

Stephen,

Well, there would have been no harm at all in option #1, which was
the most conservative of your options in many ways. There are times
that we’ve actually run flasks through multiple burnouts on purpose,
if the item being burned out was a “dense” organic, for example, or
had a high plastic content. It doesn’t hurt the investment or
decrease the reliability of the casting to do so.

I’ve not tried to hold flasks for multiple days at a particular
temp. While I suspect you could do it, the electric bill would be
pretty high!

Finally, your third option has a lot of variables in it. In
open-crucible melting, you need to be suRe:

  • the metal is clean and well-fluxed with borax,

  • has reached a really good flow temp without overheating,

  • is poured steadily and quickly enough that it isn’t freezing along
    the way,

  • is being poured into a flask whose temp is high enough to prevent
    premature freezing (900 F)

  • has enough force, either through vacuum or centrifuge, to vent the
    air trapped in the casting area through the plaster and encourage the
    metal to flow into all the spaces of the casting.

In a vacuum caster, that’s why you’re using perforated flasks. If
you’re trying to achieve the same thing with a solid flask in a
vacuum chamber, your results are likely to be inconsistent and not as
good as with perf flasks.

I hope this helps! It’s based on my experience, but others may have
different opinions based on the specific equipment you’re using.

All I can say is “i hate it when that happens”!

Karen Goeller
No Limitations Designs


#3
So now there are 5 flasks, that represent a lot of work waxing,
and no chance of repairing the machine until Tuesday. Each casting
was about 300 grams of sterling deox. My question for the casting
sages on the list is what should I have done? 

Stephen, Boy, stuff like that can really feel like a kick to the gut
can’t it?Had it been me I would have let the remaining flasks cool
down as slowly as possible,then when you can handle them, you wrap
all the flasks in a damp towel (although some don’t) and let them
sit there as long as you want. I have seen flasks cast after sitting
a year on the shelf with no problem. You just can’t knock them around
or you’ll risk breaking off detail inside the flask if the wax is
melted out already.If the wax hasn’t been melted yet I do recommend
moistening the investment over the course of a day with the wet
towels as this seems to sort of condition the investment and the
steam created helps to evacuate the wax. Anyway, next time don’t
feel pressured to cast right then if you can slowly cool things down.
Thats my experience anyway. In Carson City, Nevada where the snow is
flying again.(they’re saying this storm may span coast to coast in a
few days time.)


#4

If you can keep them at casting temperature till your element
arrives that would be the best solution. If not cool to room temp
slowly and reheat by following standard burnout cycle.

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550


#5

Stephen,

So now there are 5 flasks, that represent a lot of work waxing,
and no chance of repairing the machine until Tuesday. Each casting
was about 300 grams of sterling deox. My question for the casting
sages on the list is what should I have done?

I have had my kiln coils go out many times while burning out 3x7
flasks with 50-70 pieces in each of 9 flasks. Just let them cool and
then just bring them back up to casting temp, hold about an hour and
complete your casting as usual. I have never had any problem doing
this. What caused my problem was I had the flasks to close to the
wall, the reflected heat at 1350 melted the coil.

Richard Hart