Re: Molding Sand


Posted by Hank
on February 15, 19100 at 21:58:44:

In Reply to: Molding Sand posted by Glenn
Duncan on February 15, 19100 at 20:54:05:

what is in casting sand?
a formula for mixing your own?
Is there a formula for casting sand?
Is kaolin the bonding agent?
Is it really green or is that a term for unfired?
The finer the sand in the mix, the finer the detail etc., but is
there a problem with using fine sand and a recomended
particle size?
Kaolin is not a good binder I don't think. as pointed out bentonite
is better, stickier; green refers to unfired; don't use sand finer
that 120-140 mesh for the finest castings, average mesh runs around
80 (for steels) to 120 (for bronze and aluminum)

There are all kinds of ways to cast metal in all kinds of
Casting sand is basically a mixture of sand (which provides the
base), clay (which sticks the base elements together) and something
to wet and swell the clay and make it sticky. The easiest route is
to go to a foundry supply house and get some premix of some sort.
Petrobond premix uses an oil to swell the
modified bentonite clay. The premix can be used without any further
prep like mulling. The sands refered to in the previous posts were,
like petrobond, synthetic or put together from components. When you
get into sands Designed for special purposes like steels and
different pouring conditions the list of additives can get

The "natural bonded" sand I refer to in my original post is
and clay mined just like that from the ground. I have tried going
out in the back yard and digging some sandy soil, sifting out the
lumps and packing it into a mold. After a suitable period to dry
out the surface a bit I then poured metal and had some fine
castings. (It is not necessary to dry sand completely. In fact a
little moisture at the metal-sand interface can create a smoother
casting. Too much and it will blow holes in the casting or
mold). Some commercial natural bonded sands (such as the
"French sand" of the Getty foundry in Williamsburg have as much as
20% clay in them and need to be dried before pouring.

I am designing a piece of sculpture that will require some
sections which will be welded together to form a spherical form. I
think that Mike's claim that a casting of 3' will run easily is
good. I will be looking for 4' and I believe now that it will be
possible. I have actually seen flasks for large sheet forms and an
old foundry that were 4' by 8' but I never saw the castings made in
them. I am now on a quest for the sand I saw in a Tulsa
foundry (Leo Smith's place). The sand was called Kansas City
and came from somewhere near KC, KS. I believe the clay content was
about 10-15% So, get a shovel and find some nice looking dirt
somewhere. Find a clay test kit or wing it. and also find a casting
flux for those pistons.
Call any foundry supply house near you.

Hank Kaminsky, Sculptor
Studio: "The Art Experience," 641 West 6th Street,
AR 72701
Studio 501-442-5805, FAX 501-582-1262 1-888-776-7282

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