I checked the archives for on making a steam de-waxer,
and learned quite a bit. However, I still have some questions.
Someone mentioned the possibility of using an inexpensive electric
roaster as a means of dewaxing, but there was no as to
whether to use it dry (as a regular roasting oven), or to put the
flasks on a rack above some water and use it as a steamer. Also,
would one be able to generate enough heat to melt carving waxesi.
Someone else mentioned that one could rust out their kiln if the
flasks were put in directly after steam de-waxing. If this is the
case, how long should one wait before puting steam de-waxed flasks
into a kiln i. Other suggestions were using large pans with racks to
keep the flasks elevated above the water, and to steam for an hour.
However, the problem would be that there would not be enough heat to
melt carving waxes.
Several mentioned the use of a pressure cooker, which seem to me to
be ideal as it creates steam hot enought to melt carving waxes.
However, the pressure cookers that I saw, seemed very large, heavy
and expensive. Are there any alternatives to them.
If a pressure cooker is the most feasible way to go, what pressure
should one use, and how long should one steam the flasks.
Steam dewaxing is far superior to dry dewaxing no matter what you
apparatus you ultimately come up with to create the steam.
Here are some of the very distinct disadvantages to dry dewaxing–
takes at least 2 times longer is messy to deal with wax residue is
smokey smoke and wax splatter eat away heating elements if using
electrical means of heating evrything seems to get coated in a nice
crappy char
Steam dewaxing will not rust out your burnout oven/kiln any sooner…
I’ve been steaming for 10 years in a home made steamer and using the
same commercial gas fired oven. The rust that’s taking place is from
the water of hydration escaping the burnout temps. We used to do
100% dry burnouts “back in the old days” in a burnout oven and it
was a super duper mess compared with steaming…burners got
clogged, vent pipes coated with black and brown char, smokey ugly
environment during the melt out phase, and dripped wax all over the
place.
If you use/make a cabinet/chamber style steamer the overall
enclosure needs to be a snug but not air tight fit…don’t want to
build unmanagable pressures. We built our homemade steamer (the Mark
I) from a normal steel split 55 gal. drum with legs welded on and a
larger gas hot water heater as the burner. It’s been functioning
daily for at least 8 years but is seeing some rust on the
un-waxcoated surfaces. Will be getting replaced this summer with the
Mark II. We made a larger steamer ‘cause we can steam out up to 15 -
6X6" flasks at a time (takes about 3.5 hours up here at 5500’
elevation where water boils at around 200 degs F. This boiling
temperature means normal carving wax won’t melt readily and because
of the small amount concerned, we just put it in unsteamed in the
regular burnout cycle.
As to using a pressure cooker…don’t see why it won’t work…
large autoclaves (giant pressure cookers) are used all the time for
larger industrial/sculpture lost wax casting. Greater pressure means
higher temps and shorter times. BUT greter pressures means greater
risk of a mishap. Can’t give you any specific help here but you
might want to search the archives at http://www.artmetal.com/front_page
From Albuquerque at the southern end of the Rocky Mountains…
Frank
I have dewaxed flasks very successfully with a Baby Burco, I don’t
know if you get these in America but they are an aluminium or
stainless steel drum with a heating element in the bottom. They are
used for boiling clothes, or in canteens for boiling water in bulk
for making tea. You often come across them at car boot sales in the
UK. You make a grille that stands about 6" up from the bottom inside
and then put 4" of water in and heat and keep just at a boil. The
flasks go hole downwards on the grille so that the boiling water does
not reach them and left until the wax has melted and poured out (
maybe an hour ) it depends on how big the flasks are, not very
critical. The idea is to keep the flasks saturated with water so the
plaster does not crack. You then put them stright in the kiln and
fire using your usual settings. As far as rusting the kiln elements
you are not putting any more water than usual in the kiln and I have
never noticed any damage. When you have finished steaming switch it
off and when it is cold just crack away the thin sheet of wax that is
left. DO NOT let the steamer run dry or you risk heating and igniting
the melted wax.
I will start by listing the temperatures of condensing steam qt
appropriate temperatures:
1 atmosphere ( 0 psig gage) 212 F
5 psi gage 227 F
10 psi gage 239 F
15 psi gage 249 F
100 psi gage 337 F
Domestic pressure cookers may be capable of working to 5, 10 or 15
psig maximum pressure.
Generally industrial de-waxing using ceramic shell investment can and
will nominally run at about 100 psig. This industrial melt out can
takes less than 30 minutes.
This is very effective at rapidly removing molding waxes and the
harder waxes used for industrial parts These are similar to the
machinable carving waxes. These temperature does not totally de- wax
the mold. Efficiency depends on the actual mold configuration for
fluid wax drainage.
Poor Sprue configurations can cause some wax to remain in trapped
sections which may cause problems. Complete wax removal is conducted
during burn out which ends with mold vitrification with ceramic shell
investment. With ceramic shell temperature rise are very rapid.
Gypsum plaster investments can not go this high and ass fast and high
temperatures in burn out attempts are destructive too the mold.
Organic compounds generally decompose to carbon above about 450 F.
Ray Bradbury’s classic “Farhenheight 450” refers to this. To removing
(burn out) of the carbon requires combustion with oxygen and molds
can be very inefficient at getting air into the mold raising the
temperatures increases burn rates but does not get oxygen to the
right places quickly. Soaking time helps as air slowly diffuses thru
the mold. Remember that combustion products fill the mold with oxygen
poor gases.
Higher temperatures do not increase this very much. and can damage
the mold surfaces. Many of the recommended practices tend to go too
high too fast for gypsum based investments. Consider this if your
practice gives difficulty. 1200 F is a recommended maximum finishing
temperature and may be too high, soaking at 700- 900 F for a period
with only a short finish at a higher temperature may work better for
you. It definitely does on very large gypsum molds. Steam de-waxing
helps by driving steam through the molds and greatly reduces wax
absorption into the mold. Starting with a wet mold and slowly heating
to above 450 F helps. In this regard initially de-wax above boiling
water. when wax appears to be gone start with the final slow burn
out.
I haven’t tried either the electric roaster or the pressure cooker
methods, but I’ve had good success with plain old enameled pots.
First I used a spaghetti pot with a strainer pot that sat inside it.
I put that over a single burner hot plate with a couple inches of
water in the bottom of the pot. It worked great, but it could only
hold four 2 1/2 inch flasks. But my kiln could only hold 4 flasks, so
that was fine until I got a much larger kiln that can hold sixteen 2
1/2 inch flasks in one layer. Then dewaxing four flasks at a time
just took way too long. So I went shopping.
I bought a very large canning pot with an inner rack meant to hold
canning jars. I got it at a thrift store for $6. I found a large
round wire cake cooling rack at a dollar store, and wired that firmly
to the canning jar rack to create a stable platform upon which to set
flasks. It holds them about 3 inches above the bottom of the pot. The
large canning pot holds sixteen of the 2 1/2 inch flasks. I put in 2
inches of water, add the flasks, and put the whole thing on the side
burner of our outdoor propane grill to dewax. (The little hot plate
just can’t heat that much at once).
It takes about 2 to 3 hours to dewax that many flasks at one time,
and it’s a bit of a PITA to haul the heavy filled pot up and down the
steps to and from the shop. But it’s worth it in terms of how much
less wax smoke ends up in my house/shop during burnouts despite the
large ventilation fan right above the kiln.
I have to wonder if the pressure built up in the pressure cooker
might not damage the plasteri Unless you leave the valve open. I have
a steam dewaxer…they are great! They remove most of the noxious
fumes that you otherwise get with burnout. The only disadvantages are
it’s an extra 2 hours added to burnout time and 2. you cannot use
it with most carving waxes…most will not melt out at steam temps.
You could probably use an old oven with a pan that stretches across
the whole width/depth of the oven, fill it with water and the flasks
on the shelf above iti Try Goodwill or some other thrift store!
You could do what I did…I checked with Rio for a used/demo model
and got it that way at a discount. I believe Gesswein also has
used/closeout/demo equipment.
Several mentioned the use of a pressure cooker, which seem to me
to be ideal as it creates steam hot enough to melt carving waxes.
Steam dewaxers are only good on low melting temperature waxes like
injection wax and sprue wax. Carving waxes melt at approximately 240
degrees, well above the boiling point of water. Attempting to steam
dewax any carving waxes can result in spauling (which causes a rough
thickened surface on your castings).
Kate Wolf in Portland, Maine hosting wicked good workshops by the
bay.
I use a large pressure canner because of the size and number of
flasks I dewax. It comes with a platform to keep the flasks above the
water. I keep the relief valve open so the steam escapes. Takes 15 to
30 minutes after the valve starts hissing to do 6 3"x7" flasks. I can
invest, wait about an hour, dewax, put the flask in a 300 degree oven
and go from there.
Steam de-waxing works great! I started doing steam de-waxing in a
big enameled pot on a hot plate with flasks held above the water on a
wire mesh. When I went to work for a commercial caster we decided to
steam de-wax to lessen the amount of burning wax fumes being vented
in to the air as we were doing 20-40 4x9 flasks every evening and
generating lots of smoke and fumes.
We found that the parts that were cast from steam de-waxed flasks
would sometimes exhibit rough surfaces and even spalling of the
investment. The problems were mostly located in the areas farthest
from the sprue opening up at the top of the tree and were most
common on flat thin parts but it did happen on other parts as well
but always near the top of the tree. The theory we developed was that
the wax in the tops of the flask was melting before the sprue rod had
melted. The pressure from the expansion of the molten wax in the
pattern was breaking down the investment as it could not escape down
the sprue or into the investment because the investment was
saturated with water from the steam. We found that we could eliminate
the problem by either slowing down the rate of temperature rise in
the steamer or keeping the temperature at about 180F in the steam
chamber. Either way the main sprue had time to melt out and relieve
the pressure on the cavities in the flask before the investment was
damaged.
While I never saw this in my small studio casting flasks done in a
pot on a hot plate it was a problem in the larger flasks at the
casting shop. This may be due to the much higher power that the
commercial steam de-waxer had and the more rapid temperature rise or
it could be just the larger flask size. Either way if you find your
steam de-waxed flasks having poor surface quality slow down the rate
of rise or run the de-waxer at a lower temperature.
Jim
James Binnion @James_Binnion
James Binnion Metal Arts