Hello everyone, I had a quick question related to lost wax casting.
During the burnout session, do I keep my wax in the kiln the entire
time (even when it’s 1350 degrees)? Or do I pour it out midway
through? I’m confused because one guide on lost wax casting I read
said to keep it in there the entire time, but another said that it
can cause carbon damage to the kiln.
Thanks, Jane
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I leave it alone during the burnout. It burns out completely and I
have never seen any damage to the kiln. I put mine on auto, turn on
the ventilator and leave the casting studio until it is about the
time to cast. I do check on it off and on for safety sake.
I have a friend that has a tray that catches the wax at the 700 deg.
point and removes the tray. She doesn’t like the smoke generated in
her garage.
I can absolutely guarantee that there is no wax at 1350. Most of the
wax is melted and either is absorbed by the investment, or drained
and burned from the flask, or just plain burned off by the time the
kiln is up to 500 degrees. Your flask may be a bit cooler than the
kiln temp because it may still have water in the investment at 500
but that will soon match the kiln temp. I’ve never heard of "Carbon"
damage to a kiln, and as long as you don’t overtemp it, it will last
a long long time.
Jane, There are two answers. Casters doing large amounts, and needing
to control burnout fumes, can use steam dewaxing to melt out most of
the wax prior to burning out the flask. The steam will melt normal
injection waxes, but is not effective for most of the carving waxes.
With steam dewaxing, the majority of the wax is removed before the
flasks even go in the burnout kiln.
Once the flasks are in the kiln, though, you leave them there. “even
when it’s 1350 degrees” suggests you may not have realized that by
the time the kiln reaches that temperature, there’s no trace of wax
left. It’s gone. At that point, you’re simply burning off residual
carbon in the molds. The injection waxes themselves generally melt
around 170 degrees F, carving waxes are in the mid 200s. You could,
if you wished, place the flasks on some sort of tray for that initial
heating stage, and remove the tray after a suitable amount of time,
along with the wax that has by then run out of the molds (you put
them in the kilns sprue hole down for just this reason) There’s no
point where the molds would ever be full of wax melted enough for you
to pour out, since as it melts, it flows out on it’s own already.
Most small volumn casters don’t bother to worry much about the wax
that flows out into the kiln. It burns off just fine.
As to carbon, one of the key differences that may exist between
kilns intended for wax burnout, and those used for other things like
enamels, is that burnout kilns need sufficient air flow to keep a
supply of oxygen in the kiln. If the kiln is designed right, then the
atmosphere in the kiln will remain oxidizing throughout the burnout,
thus eliminating any carbon that exists as a residue from the wax.
The reason for holding the 1350 temp for more than a brief time is
that some of the carbon will be imbedded in the investment from when
melted wax was absorbed by the investment, and this carbon takes a
bit longer to fully burn away. That within the main kiln chamber is
gone before you even got to 1350, and in a properly designed burnout
kiln, the carbon does no damage to the kiln. Eventually, the heating
elements burn out, but that’s due to oxygen and general degredation
of the element just from heat, not because of the carbon from
burnout.
most commercial casters remove the wax by steaming it out. This
recovers the wax and means there is less to burn. Your wax will melt
at about 140F so if it is a large piece you can heat to that and pour
it out. Finer detail work you just use a suitable temperature
gradient to ensure that it all burns out as some will be adsorbed
into the investment. Electric kiln elements develop an oxide coating
on them and carbon reacts with this and this leads to thinning of
the elements. Your wax will be gone by that point if you ventilate
your kiln.
I have a Paragon programmable kiln which I use for wax burnout. The
instructions are very specific and state that the wax should be
removed as the carbon will damage the elements.
I have a Paragon programmable kiln which I use for wax burnout.
The instructions are very specific and state that the wax should be
removed as the carbon will damage the elements.
I’ll bet your kiln was originally intended for ceramics, and not
intended to maintain an oxidizing atmosphere during burnout. In that
instance, exposed elements might be affected. But I’ve never seen
such instructions on a kiln actually designed primarily as a burnout
kiln.
One more thing to consider, if you are handling the flasks while the
are hot, you also run the risk of crumbling some of the detail
inside of the flask. Just leave them alone and they will be fine.
Most elements are inside of the lining of the ovens and will be fine!
I'll bet your kiln was originally intended for ceramics, and not
intended to maintain an oxidizing atmosphere during burnout. In
that instance, exposed elements might be affected. But I've never
seen such instructions on a kiln actually designed primarily as a
burnout kiln.
All the small electric burnout kilns I have seen do nothing to ensure
a oxidizing atmosphere during the entire burnout cycle. To do so
would require a fan to provide a constant flow of air into the kiln.
During the initial stages of burn out the atmosphere in the electric
kiln is definitely reducing. Carbon monoxide is produced during the
burnout and this will reduce the metallic oxides on the heating
elements which shortens their life. But that said the typical use of
these kilns is such that this does not translate to a real problem
for the majority of users. Unless you daily fill your kiln with
flasks you likely will not have a problem. Most industrial users who
would run into more problems with this use gas fired kilns as the
cost of running them is so much lower than electric ones. If your
kiln has exposed elements that can be replaced then this is not
really any issue as the element cost is quite low. If you have a
ceramic fiber muffle in your kiln then you will have to replace the
whole muffle and this is quite expensive. But overall I think it is
really a non-issue for the majority of small volume casters.
My Paragon programmable kiln is made for wax burnout. The model is
Express E-12T.
It can be used for glass, enameling etc,but is made specifically
for wax burnout. I use a tray over which is placed a wire grid. The
flasks are placed on the wire grid, sprue hole down, The tray can
easily be pulled out from the grid to remove the wax, leaving the
flasks resting on the grid. I did call them to inquire about having
to remove the wax, and they repeated what was in the manual—remove
the wax, or the exposed elements will be damaged. Obviously, other
kilns do not require removal of the wax, but mine does…
The instruction specifically say that the a wax tray needs to be
used and removed after the first stage of the melt off is done and
that extensive carbon will damage the interior of the kiln.
I use a kiln for burnout that was probably designed for ceramics or
enamelling, and I had to replace an element (the coiled wire that
provides the heat) because it melted due to wax fumes causing a
reducing atmosphere in the chamber. Since then, I’ve kept the door
open a crack until the visible smoke stops coming out (around 650F)
and closed it after that. So far, this has worked fine, and I
haven’t lost any more elements. If you don’t want to have to do that,
steam the wax out of the flasks before the burnout. I’ve done that by
putting the flasks on a rack over an inch or two of water, inside a
large electrically heated covered roasting kettle (which are also
used for deep-fat frying, although this one is only used for
dewaxing). It doesn’t seem to affect the quality of the castings to
do this, but there is an upper limit on the size of flasks it can
hold.
This is once again a case of some engineer stating something they
have no experience with.
ANY burn out oven will survive this, with exposed element wires or
not.
The damage that occurs in most ovens is the moisture leaving the
burn out chamber will eventually rust the metal out. This is by a
vent hole or door opening. This take many years in any of the ovens
used for casting. The other damage is having any unit left on high
and forgotten about. This is like a recipe for a melt down.
In forty years of casting I have gone through about eight ovens. I
have used gas as well as electric kilns. I have had new and used ones
of various brands. I have replaced the element in electric ovens
three times.
Ney builds a great little oven. The larger ones should be 220 volt
to save money. You should get at least ten to fifteen years out of an
oven.
A kitchen stove hood will vend most burnout ovens adequately. I
prefer VentAHood brand kitchen hoods. I have four hooked up in a row
and can turn one, two or all of them an as needed.
I have great respect for Peter Rowe’s opinion. He seems technically
right on. But I would like to suggest and additional modification to
burnout procedure to help with the wax smell and smoke.
During a discussion with the retired director of research at Ransom
and Randolf he suggested that I try out a fast burnout procedure with
the kiln pre-heated to the final burnout temperature of 1350 F (732
C). I get no smoke and practically no smell. The complete process and
scientific argument is presented on my blog:
Please go there and see the discussion. Also, please note that I
mention the importance of venting the kiln (cracking the door, if
necessary) to allow oxygen in to oxidize the carbonized wax.
I am uncertain about the discussion about damaging the heating
elements. I usually use a Nyecraft Kiln with enclosed heating
elements. However, I once had a kiln with exposed heating elements
and these became brittle after being heated and I had to replace them
after a trip with them vibrating in the truck. This may well vary
with the different heating element composition.
Peter, I would appreciate your comments on this discussion.
The damage that occurs in most ovens is the moisture leaving the
burn out chamber will eventually rust the metal out. This is by a
vent hole or door opening. This take many years in any of the
ovens used for casting. The other damage is having any unit left on
high and forgotten about. This is like a recipe for a melt down.
Make the bloody box out of stainless. Slightly harder to work and
more expensive but in decades it will still look the same. A good
investment.
Former wife has a big pottery kiln clad in stainless but the silly
buggers used mild steel for the bottom. Out of sight and out of mind.
Enough rust and I was afraid to even move it, and I don’t scare easy.
For melt downs (I have experience just don’t uses nichrome
coils. Pottery supply places will wind you new coils…with Kanthol
A1 or better. Price is quite reasonable. My little over powered kiln
flattens out at 2400 F. No damage done. A few extra $$ for premium
materials and it is still happy after 30 years. Making kilns is a lot
of work and fixing them is a real pain in the ass.
I have modified many a machine in our little jewelry world, but I
would not try to make a burnout oven.
I use the ones commercially available, and many times you can find
them used and in somewhat good condition at a reasonable price. Half
of the ovens I have owned where purchased new or I got them for free
or from someone going out of business. They are easily fixed in my
opinion and quite durable except for the rust out part.
If the oven makers would make them out of stainless steel they would
never wear out. Maybe the same reason cars are not made of stainless.
I have never in my experience had to have an oven get hotter than
1600 F. When enameling, I have used an open top enameling surface
only for that.
If you can make an oven, more power to you! I myself would not.
Best regards,
Todd Hawkinson
Southeast Technical College
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just don’t uses nichrome