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.