This specific problem you describe sounds like an incomplete
burnout. I would guess that the caster may have consulted the grower
but did not follow instructions in detail, and if the instructions
are not followed in detail, the casting will fail.
The different resins have different castabilities, And several are
very castable"Invision HR, Perfactory", We have found no ash content
in Invision HR resin using a full burnout process. Some are castable
but with a bit of work around(Viper). We cast primarily Invision HR
resin. Of note is that we often cast hand carved waxes right along
with the resin with equal success.
There are very specific steps to take in casting the materials. A
caster must want to change some steps to have a successful casting of
resins. Most failures occur because the caster will not adapt the
process to the material, they insist on using methods that work with
wax, but just wont work with the newer materials. Skipping any of the
steps will definitely result in failure.
It took us a bit of trial and error to dial in casting of resins.
From experience, the biggest problem is the investment and then the
burnout. I will briefly cover some of the primary details of the
Sprueing is the most overlooked part of casting in many cases, A
smooth transition from the sprue to the piece to be cast is
essential. The piece needs to sprued at its heaviest section, general
sprueing techniques apply here.
**Viper models are castable but need a extra blowout sprue to assure
full cleanout of the cavity, there is the possibility of ash in viper
models. Prior to casting, the cavities are blown out with compressed
air to make sure all Viper residue is gone**
The choice of investment is one of the most critical steps in the
process. We have tried many investments and many processes. These
steps work consistently in our production. We use "Doc's Plaster"
from PM West for all resin casting, it works for gold silver and
platinum we follow the directions as specified by the manufacturer.
We use the rubber flasks as supplied by PM West for investing. For
smaller castings we use a yoghurt cup that we cut the bottom out of.
We do not use a metal flask, all castings are done "flaskless" Its OK
to use a debubblizer solution.
Yes, the investment costs more than regular investment, but getting
the casting right every time is worth it.
We burn out with an electric oven with a programmer. ( Gas ovens
naturally have enough oxygen to get a good burnout) We have modified
the oven by drilling four holes into the kiln at floor level, equally
spaced. We drilled about 1/4 inch holes. To increase the ability of
the oven to truly burn out the resin, the oven needs more oxygen.
To create the proper burnout, We use an old aquarium bubbler as an
air supply. We attached about a foot of quartz tubing to the plastic
hose and insert the quartz tubing into one of the holes we drilled.
This is probably the most critical step in burnout, electric ovens
do not have enough oxygen circulation for a good burnout. Heat alone
will not fully burn the resin. Our burnout schedule is ramp to 300F
hold 1 hour, ramp to 600F hold one hour, ramp to 1500F hold for
three hours, ramp down one hour to 1100F or your desired casting
temperature. You can actually do a three hour or so burnout if your
in a great rush, but in general we recommend the above. The lower
temperatures are very important and should not be rushed Casting we
cast with a centrifugal casting machine or for platinum the
traditional upright machine.
We cast many ounces of Gold and Platinum every week for large
accounts and have a very high success rate, and failure is usually
based on traditional casting problems such as sprueing, too cold
metal, Flask temperature, etc not the resin.
The models can be molded, but unless you need a mold there is really
no need to make one. The casting of resins is a more scientific
approach, but easily achievable.
This has been very brief, but gets the process pointed in the right
direction. Again the right investment and the proper high heat
burnout with air itroduced into the kiln are the primary factors in
Contact us with any questions.
Thomas Cavagnaro, G.G.
Cadsmithing, LLC, A Service Bureau
CAD-CAM, Casting in Gold and Platinum for the Trade
480 632 1595
Fax 480 632 1598