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Ceramic Shell Casting


#1

Have any members utilized the ceramic shell casting technique?
In this process, a wax crucible is attached to the wax model, and
several layers of colloidal silica and molochite are applied.
The wax is burned out with a torch and metal is melted in the
attached crucible, flowing directly into the mold. Is anyone
aware of any other “investments” or slurries that can be used for
this unique process? Marty R.


#2

Marty,

I have a art bronze foundry and use the ceramic shell process.
I use the coloidal silica along with fused silica flour for the
slurry. For the first 2 sand coats, I use zircon sand, for the
remaining coats (about 5 or 6) I use fused silica (35-50 mesh).
There are a number of coloidal silica mfgrs (ranson & Randolf and
REMET are 2). There are a number of different sand and fillier
materials too, depending on the metal to be poured.

I do not know about melting the metal in the cup. The wax is
melted out, the shells have to fired (I go aobut 15-20 minutes at
about 2000F or until the carbon is nearly gone, repair any cracks
and fill any drains, then fire again for 10-15 minutes just prior
to pouring and pour into a hot shell. I do have a cup form at
the top of the sprue, something to pour the molten metal into. I
melt in a crucible (currently about 85 lbs but soon up to about
300 lbs/pour). I pour directly from the crucible into the shell
form. If cast iron is used, it is often (usually) ladeled into
the form.

Mud can/has been before ceramic shell came about. Some have
played with raku type clays, incorporating straw and the like for
steam venting. “Home made” investment mixes are used by many
with as many or more mixes of just about everything, being used
in the investment. Needless to say, some work better than
others.

John D.


#3

John, as it so happens, I came upon a description of this
process which I had bookmarked long ago from a site on bronze
casting–you’re a veteran but others may find it interesting
http://www.andrewdevries.com/overview.htm MDR


#4

Good morning:

Trevor F. posted an accurate description of ceramic shell casting.

Ceramic shell is the dominant process for making industrial
investment cast parts. Generally, the “tree” is about three to four
feet long. Solid mold is not practical in many applications due to
shear size and other factors. The process of dipping, coating and
drying is a long slow process and as such, not practical for the
small trees used in jewelry casting. Several grain sizes of silica
and other refractory materials are used in making the tree and are
generally purchased by the truck load. A typical binder is
colloidal silica, which is used with dental phosphate investments
and with some of the platinum investments sold in our industry.

Industrial suppliers of these materials would be Remet Corp. in
Utica, NY and Howmet-Alcoa in Cleveland, Ohio. Remet does a good
job on their website http://www.remet.com where some insight is
given relative to art applications.

Give me a call on the 800 line and I will answer your questions more
in depth.

Regards,

Bill Mull
Zero-D Products, Inc.
Precision engineered materials solutions
800-382-3271 in USA, Mexico and Canada
440-942-1150 International
WWW.ZERODPRODUCTS.COM