On 28 Feb 2004 09:36:34 -0800, (Leon McAtee)
wrote:

===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.
===
============================
===Leon McAtee

If you mixed your greensand correctly I would not fool with it. When
you cut your sprue and gate and runners are you slicking them down and
making it so there are no sharp projections into the mold cavity that
can get washed off. At the bottom of the sprue you need to make a
deeper impression so the turbulance of the molten aluminum does not
cause the sand in this area to get erroded away. Simply make a deeper
cavity below the bottom of sprue and also below the bottom of any gate
or runner. I think the 10% of bentonite to sand is in the ball park.
70 mesh is pretty coarse so you may want to add just a touch but not
all that much more bentonite.

Another last ditch effort is to make a vent riser equal in size to the
fill sprue, and tilt your mold so this vent riser is at the higest
portion so any loose floating sand is floated up and out this vent
riser. Its not a cure but a possible work around. Make sure your
ramming the mold sufficiently and slick down the edges of the pattern
/ mold at the parting line so it does not contribute to loose sand in
your mold.

Pouring thinner sections hotter is the normal proceedure.
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