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Warped flasks

Hi folks

I have had at least 3 or 4 bad castings on my vac. machine over the
past 6 months. I finally switched to one particular perforated flask
which worked for me and things went well. Last week I decided to
cast two flasks on the same cycle. One of them was my trusty old
flask, the other was brand new from Stuller. (Roughly $45) The
first casting went perfect. Really didn’t even have to tumble. The
second one, (new flask- same size) couldn’t pull the vacuum up. I
can’t remember exactly what the gauge said, but it went only maybe to
5 or 7 lbs. (? I think) while the first one slowly rose all the way
till it was pegged. I tried pushing down on the flange of the flask
with my long tongs when I realized that the flask was rocking on the
flange. I pulled the flask out of the machine (scrambling at this
point) put on a second small gasket. Still no luck. I decided at
the point I had nothing to loose, so I melted the metal and cast it.
The piece was over-sprued and it did form with very minor porosity.

My question: Has anybody had this kind of trouble before? This is
probably the 3rd flask now that isn’t usable (unless this is operator
malfunction) and each time it costs me the wax patterns, time,
electric, plus the cost of the flask. I’m looking for a solution to
this problem so if anybody has any ideas I’d appreciate them.

-Stanley Bright

Perhaps what you need to do is preheat the flasks empty, first. It
is possible that the flask edge is cooling off more rapidly because
of a small leak and the heat change might warp it… check the flask
and make sure there are no burrs or hang-up… Ringman

Was the flask seating areas checked for parallel before heating?
Normally the lip on those flasks is pretty thick right at 1/4 inch
and they shouldn’t warp especially if the metal is a good quality
stainless steel unless they are getting way over heated , but then it
seems you would have investment break down. Beyond that is the
seating are was never flat and parallel to begin with. If you know
someone with a lathe, you could have them true the face for you, I
had some similar trouble a few years back with some perforated flasks
I bought from Swest, That was the last time I tried to save a few
dollars. I’ve been using flasks from Rio Grande, and not had any
problems, other than affording them. I choke every time I open a
tool catalogue…