I’m just getting into lost wax casting and I have a question about
burnout temperatures and times. I have seen tables in well known
books calling for an hour at 300 degrees F, an hour at 700, two
hours at 1350, with a subsequent reduction of temperature to 200
below the melting point of the metal (these are approximate values
from memory). Initially, at least, I just want to cask prototype
pieces in small flasks using a Kerr centrifugal caster I bought on
eBay. Yesterday I went to my dentist with an emergency toothache and
afterwards asked him about how he does burnout. He said he uses
something (I think) called “hygro burnout” where the investment is
soaked with water before the burnout and the temperature is only
raised to (as I remember) 1050. He doesn’t even use multiple steps;
just dials his over to produce 1050.
Questions: 1) are any of you familiar with the process he refers to?
2) are there reliable simpler burnout programs for the small flasks
used in spring wound centrifugal machines?
By the way, eBay is certainly a good way of buying some of this
equipment. Kerr Centrifugal machines constantly appear. I bid about
4 times and lost before getting one for about $80. However, I found
small ovens sell for high prices on eBay and I saved by buying a new
one from Aims Kilns in Oregon aimkilns.com for about $180. EBay is
also a good place to find relatively inexpensive vacuum pumps. I
bought a vacuum table from Rio Grande but after receiving it and
examining it, it looks so simple that I think it would be easy to
make one for a fraction of the cost. Several books have
instructions.
Russell - The bigger your production, the more a burnout cycle makes
sense. We cast pretty much like you do most of the time - 1,2,3,4
small flasks. There are people casting 100 flasks a day, and that’s
different and EVERYTHING matters more. We put the flasks in the kiln
at 5pm or whatever, and have a heavy-duty timer, the kind that’s an
electrical box hard-wired into the circuit, not one that plugs into
an outlet. It comes on at 12pm and the kiln is turned to 1350F. Has
worked just fine for many years, and I discussed it with a Kerr rep
and he had no problem with it, either.
It is probably a better idea to follow the instructions received
with your investment. There are variations from manufacturer to
manufacturer.
Often called the “one hour burnout”, the dental method is a very
small, sometimes ringless (no flask) method that uses phosphate
bonded dental investment. Some major jewelry supply distributors
have co-opted this process to jewelry applications where you are
casting a very small flask. With larger flasks there is set procedure
of times and temperatures dependent on which product you buy. These
investments are used mostly for platinum and white gold. You can
find these investments at Dental lab supply houses as well as at
Jewelry suppliers.
Have you ever gotten up at 6:30 in the morning and turned the Kiln
on and leave for a while to workout and come back only to realize
you turned the knob to the high setting instead of the low??? As I
scratch my head and kicked myself I had also forgot to put the
thermostat in the back of the oven. You see this is the first time I
have needed to cast since having a new shop.Once I inserted the
needle like projection the tempature read 1500 degrees wow!
Well Ive lost that casting. Then I thought why not bring the temp
down and cast. OK. Then I realized I had,nt set up the Torch. Well I
moved all that and cast and the casting came out wonderful .With
shock miracles do happen.
Well I just cast a ring in a small flask in less than 2 hours. What
a day!
Have you ever gotten up at 6:30 in the morning and turned the Kiln
on and leave for a while to workout and come back only to realize
you turned the knob to the high setting instead of the low?
Just wait until you have the chance to compare this to how you feel
when, in the middle of a burnout cycle, you sort of wonder why it
smells rather worse than it should, and when you later open the kiln
to pull out the flask for casting, notice a weird large ring of ash
around the flask, and then it dawns on you that you put the flask in
the oven without removing the rubber sprue base…
Takes you down a notch. But you won’t be alone. I know several fine
casters who’ve experienced that little oversight. In one case, the
extra fumes set off fire alarms, and the fire department had to break
into companies office door in the middle of the night to
investigate…
And then there are the simple mistakes. Two flasks in the oven, one
to be cast in yellow gold, the other in white gold. A little slip of
the brain cells and you’ve got a bunch of castings all in the wrong
color. Murphy’s law, of course, will state that all of them are
careful hand carved waxes, rather than just mold injections, and of
course, several will be time critical rush jobs…
And then there are the simple mistakes. Two flasks in the oven,
one to be cast in yellow gold, the other in white gold. A little
slip of the brain cells and you've got a bunch of castings all in
the wrong color.
For those of us who don’t cast in gold, what happens? Does the white
gold somehow turn back to yellow or does the yellow somehow discolor
to a whitish appearance?
For those of us who don't cast in gold, what happens? Does the
white gold somehow turn back to yellow or does the yellow somehow
discolor to a whitish appearance?
This jeweler is talking about putting metal for flask #1 into flask #2 by mistake. I did it once with all silver, but the amounts were
different. Oops is right.
I was catching up on my Orchid reading and I noticed you didn’t
receive many direct answers to your inquiry about your burnout
schedule. We’ve been casting the way you will be since about 1969. I
own an Aim kiln also but I also still use the same burnout oven and
Kerr long arm centrifuge my dad bought back then. I mostly use
Satincast investment and our burnout schedule is pretty much what you
noted except we usually don’t end quite as hot. An hour at 325, an
hour at 700, two hours at 1,200, and if we are casting sterling an
ending temp of 1,000. I think 200 degrees below the melting temp of
metal is an ok rule though I cast copper with the flask coming out
of the kiln at around 1,850 and hold a reduction flame on the copper
as late as possible.
If you want to read a really good series of step by step articles
about lost wax centrifugal casting my dad wrote a six piece series
for Rock and Gem magazine in 1975-76 that holds up perfectly well
today. If you have interest I’ll send you a photocopy.
Your idea of building a vacuum table sparked some memories. We’ve
probably enjoyed building equipment as much as making and selling
jewelry. We started hobby casting by vibrating the air out of flasks
with an electric vibrator (hand massager) clamped in a vice.
Actually did an OK job. We built our own vacuum table using a
compressor from an old refrigerator. I still use it today. It’s a
little slower than something professional and modern but it still
pulls 23inHg. Someday when the compressor gives up the ghost I’ll
buy the pump I’ve been eyeing in the Rio catalog, but it’s gone over
35 years and counting.
We built our first wax injection unit out of a large and a small can
separated by plaster with Nichrome wire wound around the inner can. A
"U" of copper pipe with a cone on one end and a plunger (handle was
from the choke of a '54 Chevy) did the injection work. As we got
into more production we eventually replaced it with a compressed air
injector but the home-made one got us started. We vulcanized outside
the shop in a toaster oven and compressed with a four bolt clamping
system.
Our family history with jewelry goes back to the late 1800’s and
many times you just had to make your own equipment. My Grandfather
had Oklahoma watchmaker’s license number 0003. I still occasionally
use his home-made watch degausser and his ring welder.
Things haven’t always work perfectly. We fabricated a vacuum caster
out of box tubing, run off the same compressor as the vacuum table,
that worked - sort of - but was too slow to be effective. And the
experiments with vulcanizing in the oven at home made our 1972
Thanksgiving dinner late (we were all standing outside while the
house aired out).
Although jewelry and watch repair put food on the table, making
equipment has been just as fun. Thanks for your post jogging some
fond memories.