The prongs of the collets kept breaking. Why does the metal get
brittle after casting?
Really good question, Rahul!
What metal are you casting? !Are you using lost wax casting?
Centripetal (spin)? or vacuum casting? Do you recycle your injection
wax? What investment are you using? What is your burnout schedule?
How do you melt your metal? How do you protect the metal from oxygen
when pouring the cast? What is the temperature of the metal? What is
the temperature of the flask? Do all the prongs break? If only some
prongs break, where were those rings positioned in the flask during
casting? Is the surface texture of the cast ring identical to the
surface texture of the wax injection? Can you see the porosity in the
prongs before you bend them onto the stones? Are the prongs ever bent
before setting? (An employee once threw a load of rings in with a
load of clipped trees to tumble off the last bits of investment. The
heavy trees pounded the prongs down onto each ring. We carefully
pried them back up and were able to save about half the batch. But it
was still an expensive lesson. Could’a been worse. They were only
Could you post some close-up pictures of the problem rings on a
website so we can see them?
There are several reasons that can cause the metal to be brittle.
Your metal may have been over heated. The flask may have been too
hot. The metal may have been contaminated by another metal (aluminum,
lead…). The volume of your model may cause the weakness and
porosity in the prongs. Lost wax casting is a system. If something is
not quite right in the system, it will cause problems further on down
These are the most obvious reasons to me. I’m sure that there must
be other potential causes which someone will describe.
Chuck in Asheville where Mother Nature seems to be deciding on