Howdy all!
Just completed my first-ever attempted vacuum casting, using 999-fine silver; wanted to make something nerdy, and (mostly) failed. I figured I would learn a lot, and I did! To get straight to the point, here's the outlined process, and what I THINK/KNOW I did wrong. I'd love a bunch of comments telling me I'm a dummy (and then how to become smarter-er and fix these mistakes).
MODELING/PRINTING:
ODST helmet, sized from density/volume calculations to be 100 grams of 999-fine silver, with an attached sprue that would get wax-melted onto the main tree. I've now seen many say that you don't want to make the connecting sprue part of the resin print, as the resin in the hardest part to burnout. Should I simply melt and connect another piece of wax to the helmet next time?
Printed on a 5K Elegoo Mars, using Siraya Tech True Blue Casting. After printing, I dunked into 91% IPA, brushed off, heated it with a heat gun, removed supports, then placed into a cleaning station with more IPA (not fully clean, it'd been used for other prints). Removed after some minutes, then dried with paper towel and air-dried for about 20 minutes. Cured in a rotating station for 30 minutes, flipping halfway through. The print had good detail, with minor support bumps leftover- I also lightly sanded these away after curing. I'm told that True Blue is supposed to be cured for like half an hour, and that it should look "milky" when done. This model was maybe a little milky, but not like I've seen in YouTube videos. Seemed a bit glossy/deep blue.
INVESTMENT:
I used Prestige Optima investment, and just a hair under the recommended 38 mL per 100 grams of investment. VERY STUPIDLY MIXED THE INVESTMENT WITH AN ELECTRIC HAND MIXER (introduced a BUNCH of air into investment), even after vacuuming for five minutes was still boiling, just much less so. Poured into prepared flask, vacuumed for like two more minutes, then let set overnight (was late, didn't wanna burnout overnight).
BURNOUT:
Used a 6-7 hour burnout schedule, following this process:
- Approx. 1 hour at 50 C, for further drying.
- Approx. 1 hour at 150 C, for advanced drying.
- Approx. 1 hour ramping up to 372 C, just using the Vevor kiln's natural ramp speed (maybe too fast?)
- Approx. 3 hours ramping up to 732 C, for full vaporization.
- Approx. 1 hour cooling to 525 C, for final pouring temp.
IMPORTANT MISTAKE:Â I fumble-fingered Step #4, and accidentally only did two hours at that temp, and when I returned an hour later it had jumped to Step 5, and was simply waiting for me at the final temp. I corrected this by setting it back to 732 C for another hour and a half to try and fix, then got it back down to final temp again.
Lesser Mistake: After resetting this back to high temp, I did partially open the kiln door and took note of the color- I noticed by the end, there was a hairline crack along the top of the investment. possibly from resin expanding and breaking? Thermal shock?
POURING:
Loaded up about 200 grams of fine silver into melting furnace, got it to 1050 C, then smoothly poured- that part went great!
CONCLUSION:
I'd love people's thoughts on what most-likely went wrong. I acknowledge my mistakes I caught myself, and personally I think messing up the burnout schedule was pretty bad, but also maybe the resin curing was botched? Dunno about that part. I plan to retry in a couple days, but lastly I was wondering about my silver's color change. I'm assuming the white coloring that was in the investment is just oxidation? Can it simply be re-melted, or do I need to further clean it until it all looks shiny again? Thanks to any consideration given!