Calling All Casters… I’ve been using the following burnout
schedules for File-a-Wax (these have worked well for me). Could you
review them and give me your input- I am always curious as to what
burnout schedules the professionals use. I had a student tell me
that at 1,350 degrees F he turns the flask so that it is in the kiln
with the button up so that gases can escape from the cavity- any
opinions on this? Thank you!
9 Hour Burnout
2 hours to 300 degrees F
1 hour to 500 degrees F
1 hour to 700 degrees F
1 hour to 1,000 degrees F
1 hour to 1,350 degrees F
1 hour soak at 1,350 degrees F
1 hour to casting temp
1 hour soak at casting temp
12 Hour Burnout
2 hours to 300 degrees F
2 hours to 600 degrees F
2 hours to 900 degrees F
2 hours to 1,350 degrees F
2 hour soak at 1,350 degrees F
1 hour to casting temp
1 hour soak at casting temp
Hi Kate, Your burnout seems to be fine for any wax including carving
wax… My suggestion is that the carving wax flasks be put into the
oven at 300 oF and not into a cold oven. Carving wax has a tendency to
expand before melting out so this will help get it out of the cavity
as quickly as possible. Another suggestion is to use injection wax
for the sprues and not use carving wax sprues … same reasoning…
the injection wax will melt out first… very quickly at 300 oF and
this will allow the carving wax to expand itself out the sprue …
which releases the tension inside the cavity. Other suggestions:
Using a 38 /100 investment ratio for carving wax models is better
than using 40/100 as the investment will be stronger and will
resist breaking down if the item is a large /and/or heavy wax
pattern. Just a better Guarantee that it will come out…
What I use for Burn out: I personally prefer a ramping controller
versus stepped controls… this allows you to set your starting temp
at 300 for 2 hours… then ramp at 2.9 degrees/minute to 1350 oF (
this calculates to Approx 8 hours climb)then hold for X number of
hours at 1350 oF ( X depends on the quantity of flasks as well as the
flask size) Then a programed or manual drop to the desired casting
temp.
Hope this is helpful.
Daniel Grandi Racecar jewelry Co. Inc. We do casting in gold,
silver, bronze/brass,Pewter as well as finishing, assembly,
soldering, models by hand , CNC models, Molds, enamelling and a host
of other processes for designers and people in the trade. Contact Sales@racecarjewelry.com Tel : 401-461-7803
Hi Kate, I know you will get many responses to this. I can tell you
that the research that has been presented to The Santa Fe Symposium
for several years now says that 1350 F is too hot. You run the risk
of breaking down the investment from a chemical reaction between the
investment and carbon that is left form the thermal decomposition of
the wax. This breakdown will increase surface roughness and gas
porosity. Will you get a casting out at 1350F yes of course you will
but you will get a better casting if you limit the temp to 1250 F
and if you have really good air circulation (lots of available
oxygen to react with the carbon and convert it to CO2) in the kiln
then you can get a good clean burnout at 1150F. As for the time it
is dependent on kiln size, type of kiln, flask size, many many
different variables but When I used to do commercial casting with
gas furnaces we did 12 hour burnout cycles that are similar to yours
but we topped out at 1250F. Another thing that many casters don’t
take into consideration is how long it takes for the flask to cool
down to casting temp. Investment is a very poor thermal conductor.
We were using 3 and 4" diameter flasks and I did some measurements
of temperatures in the kiln by investing a thermocouple into a flask
and tracking it and the kiln temperature in the burnout cycle. The
flask center lagged behind the kiln temperature by 45 minutes to an
hour. So even if the kiln says it is down to 1100F degrees the
inside of the flask was still at 1200F. Casting into too hot a
flask also contributes to surface roughness and can also cause hot
tearing in thin sterling castings.
There are lots of things in this business where people will say " I
have been doing this for many years and you don’t need to do xyz to
get good results" or “we have always done it this way and it works
just fine” well in the shop we rarely take the time to do careful
experiments and so we don’t really know what difference a change in
temperature or change in procedure really makes. This is why the
Santa Fe Symposium is such a great resource for our industry. They
have people do scientific experiments to determine if things like
changing burnout temperature affects the results of the casting
process and how does it change it. Then the experimenter presents a
paper that is compiled in to a book that is then published as the
proceedings of the symposium. There is a huge amount of information
available in those books especially on casting. So if you want to do
the best castings you can get copies of the books and read them.
They are available from http://santafesymposium.com/books_videos.html When I went to my
first symposium I came back with the on reducing the
temperature of our burnout. It made a significant difference in the
surface quality of our castings and reduced the finishing time
required. We also got rid of our hot tearing problems by allowing
the flasks cool down longer so that the flask interior was at the
kiln temperature. It also caused us to re-evaluate how some of our
spruing was being done. With the cooler flask at casting time we
had some designs that were not filling because of the reduced
temperature so we had to correct that but the overall increase in
quality of our castings was significant. Jim
My suggestion is that the carving wax flasks be put into the oven
at 300 oF and not into a cold oven. Carving wax has a tendency to
expand before melting out so this will help get it out of the
cavity as quickly as possible. Another suggestion is to use
injection wax for the sprues and not use carving wax sprues ...
same reasoning... the injection wax will melt out first... very
quickly at 300 oF and this will allow the carving wax to expand
itself out the sprue ... which releases the tension inside the
cavity.
Thanks Daniel and Jim for your suggestions! I spent a day last week
at Kindt-Collins (manufacturer of File-a-Wax). It was fascinating! I
got to see how my favorite waxes are made and got to spend time with
the brilliant folks in their lab. They have a new sprue rod
(available in 3/8, 5/8 and 1/2 inch diameter) called Magna-Sprue Wax
Sprue Rods. This wax goes from solid to liquid very quickly. In
measuring viscosity- water is 1, motor oil is 500. At 160 degrees
the Magna-Sprue wax is 195 viscosity, when the temperature is raised
to 180 degrees it is 33 viscosity- quite runny- so it evacuates the
cavity quickly giving room for the carving wax to expand itself
outside the cavity, as Daniel Grandi mentions above. Best Regards,
Kate Wolf, in Portland, Maine hosting quality workshops by the bay.