Lost-Wax cast catastrophy- need explanation

Hello again,
So I was doing my first attempt at wax cast using propane for the burnout,
torch to melt right on the flask and steam to push the silver in. Followed
a book. Using 2, 14guage sprues as entry points to a 3/8" "mold". Since
I'm practicing I was simply using 3/8" wax sprue cut in 1 cm length as my
mold which equates to 1/4 ozt of sterling (give/take) with 1cm 14guage sprue
from top to feed it in a 2" x 2.5" flask. Added 1/4+ozt str to top of sprue
opening and converted to molten with torch. Waited for roll and then
applied pressure (steam) only to have the metal jump up and around the sprue
holes and run down the inside of my flask on to my fire brick. Not a damn
thing was in the mold. It appears the force of the stema drove the molten
silver up the sides and down around the area between where the investment
meets the flask and out.
What happened? Was the flask too hot? Spue holes too small? But if larger
won't the metal solidify in the sprue before the whole it liquid?
Clueless.....panning scraps from my garage floor at the moment
- Ben
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Ben, am I to assume you bypassed the USUAL investment curing, dehydration and wax burnout in a burnout oven for several hours? RichD
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No, I did the burnout over 4 hours (using recs from the book @ 1350)...it was burned out plenty and had the grey look I was told to expect.
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That steam method sounds downright scary!
I was only familiar with the sling/centrifugal casting method.
Only problem I've ever had casting was running out of investment ~3/4 through, mixed up more & added it.(electric kiln burnout, yada-yada) Bad plan - silver migrated/split through the layers. Remebered to measure thje investment properly after that boo-boo.
PS: I've always used oxy/acetylene for melting metals in the crucible
Maybe the propane has too much water vapour in it for burnout?
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Ben, I didn't catch the point you were melting on top of the flask. The steam method is always chancy at best. Build a simple vacuum table and use good investment with an open bottom flask and melt in a small hand held crucible coated with flux. This way you have time to judge the proper pouring temp. Pour into the still hot flask right from the oven. RichD
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Well after three attempts (which equates to about 18 hours of processing start to finish), I finally got it. The steam method isn't so bad and I'm told with practice can be very reliable. The issue on first attempt was sprue hole size and positioning. Too small and too spread apart. Second attempt failed due to poor seal where the steam escaped from around the cap and the botton solidified on top...and again sprue holes too small. Third attempt it was almost like I knew what I was doing. From pulling the flask from burnout to reducing metal to molten and applying steam took less than a minute.
I know this is all fundamental to you guys but for me, it's DAMN COOL!
Thanks again and later,
- Ben
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