I'm new to this "art" and have searched the Internet for info on my
problem but haven't yet found much help so I turn here.
My problem is what appears to be sand inclusions due to breakdown of
the sand when hot. I'm trying to cast some relatively thin parts and
found the only way to get the mold full is to pour a bit hotter than I
normally do. Don't have a pyrometer yet so I'm kind of guessing.
The inclusions are on the top side of the casting (floating) and
appear to just be in the flow stream above the entrance to the mold.
The last parts of the mold filled are defect free, which makes me
think that it is sand cooking and flaking of the runners after
upstream sand has had a chance to heat.
I'm using western bentonite, around 10%, and relatively coarse sand
(70). My muller isn't able to properly mix Petrobond or K-bond sand
so until I can upgrade I'm stuck with water bonded sand.
What I would like to know is if there is some kind of modification I
can make to my Gates, runners, chokes, etc that might eliminate the
problem, or trap the floating sand before it gets to the mold? Is
there some readily available additive I can use to increase the hot
strength of the sand? More watter? I have no steam problems - yet.
18 years ago