I thought I would throw this out to the group.
I am casting large silver cups - 16-24 each. overall about 3" high,
not including sprues and such.
using vaccuum assist into investment molding.
large gates from bottom 1/3 to top 1/3 of model, vented to mold
high heat in mold, center is bright pink before casting
sprues to outside of cup, and also center
wall thickness is about 3 mm
silver melted in melting furnace, to about 1,875 deg F. recycled
scrap metal did not work, last pour used 100% new metal, this worked
So, here is what is not working, and I need to appeal to the
collective 10,000 years of casting experience of the group
a) many problems with air bubbles, the huge surface area of the
outside of the cup seems to collect the bubbles during vacuuming,
without lettign them top surface. I have tried different pour
techniques, mixing by eye, using distilled water
b) center 'core" of investment seems to be cracking, leading to some
c) Would “shell” casting be an alternative than straight investment
casting? what would the trade-offs be?
thank you in advance
Mark Zirinsky, Denver, Colorado USA
"private cutter buying rouigh and collections"
or, as the case may be, “at it 35 years and I am still learning”