Metal Casting Zone

Hello, I recently obtained a vacuum casting machine and kiln. I mix my investment, debubblize, let the flasks sit over night (they're big 4"x4" flasks). After burnout I place the flasks hot onto the vacuum table and the investment immediately breaks as soon as the vacuum is turned on. Does anyone know what's wrong? Should there be more space between the wax model and the top of the flask (the piece I'm casting is fairly big)?

Hi Tyler K

Good you are trying the lost wax casting. Investment that breaks ,I would look closely at your burnout procedure. These flasks are quite large and need a cycle like I do for my lost wax 8 to 12 hours. The weak investment i would say is that the investment is heated way above the recomended 732oc for far to long. Check the temp on your furnace If the thermostate is reading wrong you have cooked the investment. Investment breaks down and cracks and loses it strength if heated over 740oC or 750oC.
You also mentioned the flasks are left over night to sit ,It could be another area to question,the flasks could be drying out too much during this time before being put into the furnace,they must remain damp. Keep the flasks wraped in a damp rag during this time. Minimum distants that models should be to the top of the flask is about half an inch, check this when doing your wax trees . Hope this helps JOHNCAST.

"JohnCast" is right-on here.

1) do not leave your flasks overnight. try to invest, wait 2 hrs, then right into the kiln for best fresh result. if absolutely necessary cover with damp towels then a plastic cover so they don't dry out, but you will notice the burn out will be gray.
2) follow burn out schedule with investment. "JohnCast" is right-on here 8-12 hrs total with no more than 4 hrs ( one hour per flask inch) at 1350 deg. max hr/temp.
3) What brand of Investment are you using? if all above is good. switch to R&R or Kerr investments. Check your water to investment calculations. not to watery, not to thick. could be cracking due to to much water. add a little less especially if your pieces are heavy. mix investment thickness due to light, medium, or heavy pieces.
4 ) leave at least 1/2" between flask and pieces and top or more if heavy.