I am planning on getting a new burnout kiln, and have been advised
that in order to protect the interior of the kiln from wax residue I
should put the flasks on a tray, and to run the kiln for 1 hour at
300 degrees, then to remove the tray and flasks and dispose of the
wax drippings. After that, return flasks to kiln and continue
burnout.
What puzzles me is that the kiln will have a top opening, presumably
to take care of fumes and smoke from the burnout, but nonetheless, I
have been told that I must remove the tray with the wax drippings. I
had assumed that the wax tray was there to catch the drippings thus
protecting the floor of the kiln.
With my old kiln, I just did the burnout, leaving the wax tray and
flasks in the kiln during the entire process. The fumes were
exhausted through the top vent.
My question is whether removing the flasks from the kiln would cause
problems with the investment due to thermal shock, or from being
handled at this stage in the process.
I just burn out the suckers. still haven’t killed a kiln in 30 years
Nothing fancy and never even heard about a wax tray in 30 years. No
rocket science involved, just run the flasks up a reasonable rate
for long enough and drop to casting temp.
Investment always comes with mix ratios on the box (follow to the
letter !!!) Burnouts are open to lots of experiments. I normally run
an overnite cycle but when rushed a 2 hour cycle usually works.
I have been handling the burnouts at the Studio at UCSD’s Crafts
Center, ever since the Kiln Minder started misbehaving.
One thing that Jay whaley has me do for sure, is to place a flat
tray below the metal shelf upon which the flasks sit. When the over
reaches 500, and you can smell the wax, he has me open the kiln, and
with tongs, remove the tray with the molten way, and put it above
the kiln, yet under the exhaust hood.
In doing this, I do not disturb the flasks, and the molten way does
not continue cooking until it is burned away. Much less stink in the
building. Burnouts used to begin at midnight and end at 8, but since
doing it manually, the burnout is during normal class hours.
well, the idea is to melt out the majority of the wax at 300
degrees…this is before the wax actually ‘burns’…so by removing it
before upping the temp, you don’t burn most of the wax, just the
residue inside. if you leave it in there, then you will end up with
some pretty bad wax burning fumes! At that temp, there shouldn’t be
any problem taking the flasks out briefly while you remove the tray,
and then putting them back. by the way, the ‘one hour’ in at 300 is
dependent upon the size of your flask. If you have larger flasks,
that time increases, as does the time for each burnout stage. If you
try to raise the temp of a flask too quickly(by using a short
burnout on large flasks, for example), you risk the steam pressure
building up and blasting your plaster to pieces.
The wax vapor is corrosive to the heating coils, and just generally
annoying, which is why most people melt as much as they can, then
pull it out before it burns away.
If you’ve got a gas kiln, you’ve no coils to worry about, so don’t
bother. Otherwise, it might be an issue to unload the flasks and
then reload them. This is why most burnout kilns have steel grid
floors, with steel trays underneath that you can just pull out
without disturbing the flasks. Not that hard to make if your doesn’t
have one already. (Go to the DIY, get some expanded metal grid,
(steel), and a couple of bits of angle iron, and some sheet iron.
Weld angle iron to expanded metal to raise it up a bit off the kiln
floor. One bit of angle iron on each side, and one strip up the
middle. (it’ll be weak when it’s hot.) Use the sheet iron to weld up
a couple of little trays to fit under the expanded metal, so that you
can pull them out once the wax has dripped into them.)
If you take the tray out you get less smoke, if you have the height
in the kiln you could rest the flasks on a grille and slide out the
tray leaving the flasks in place.
I read a report (I think in one of the Santa Fe books) about how
fast flasks cool down, it is not very fast especially at that
temperature so I don’t think you would have a problem.
Some burnout kilns have a built in wax tray that drains to the
outside, maybe you could incorporate one, then you get the best of
both worlds.
Ideally, Alma, you would have your flasks held above the tray on a
rack that allows the tray to slide out without disturbing the flasks.
This might be something that you have to make yourself. If the tray
is full width, you will probably need to narrow it. BTW, I don’t have
this; I just burn it all out in my Neycraft kiln, with a fan vent
hood above it. It’s been working fine for many years.
Considering the economy, the show was great. Was really pleasantly
surprised. My best sellers were my cloisonne pendants.
The old burnout kiln which is a Satellite, is working fine. However,
It is not programmable and I have to baby sit it to adjust the
temperature during burnout time. I am thinking of getting a Paragon
Sc3, which is fully programmable.
Thanks for all the wonderful responses to my query about wax burnout
procedures. In order not to void the warranty on the new kiln, I will
have to follow their instructions about dewaxing using the wax tray.
I think there will be enough head room in the kiln, and enough space
on either side of the dewaxing tray for me to rig up a grill above it
on which to set the flasks, and then just pull out the tray after the
300 degree burnout for 1 hour.
Or else, I will just remove flasks and tray. Tim has pointed out
that there will not be too much of a cool down when they are out of
the kiln. So that is one less concern.
As I use hard carving waxes, steam dewaxing is really not an option,
so it will have to be done according to the kiln manufacturer’s
instructions.
What puzzles me is that the kiln will have a top opening,
presumably to take care of fumes and smoke from the burnout, but
nonetheless, I have been told that I must remove the tray with the
wax drippings.
Steam dewaxer will remove the wax. The wax fumes are corrosive, to
the kiln and to you. Depending on the size of your flasks, you can
use a pressure cooker. I used one to dewax 9 3x7 inch flasks and I
did it 3 times a week for over 10 years. If you need move info= ,
email me offline.
You really don’t want to “burn” out all the wax - you want to melt
out as much as possible.
A procedure starting with wet flasks will help. This may involve a
separate steamer from the kiln or a removable drip pan.
A big problem in dewaxing is getting the mold as clean as possible
before doing any burning. Steaming does this at a lower temperature.
Steaming helps to keep the wax from adsorbing melted wax into the
mold too.
Industrial investment (different investment) casters melt out in an
autoclave with high pressure (100 psig) and high temperature steam.
This is expensive and impractical at small sizes.
Without the high pressure you don’t get a high enough temperature to
get almost all the wax.
You do not want to actually burn the wax in the kiln ( as much as
possible). The kiln requires oxygen to burn wax and all the excess
wax consumes the oxygen outside the mold.
The mold surfaces are difficult to get oxygen to as it is. Diffusion
in small passages and spaces is difficult at best.
In addition to this problem electric kilns with exposed elements
rely on the atmosphere being oxidizing for long life.
If you are burning all the wax in the kiln you are spending a lot of
time reducing. This reducing atmosphere removes the protective oxide
from the elements shortening their life with each cycle.
If you need I can dig out some book references. You probably won’t
want to buy these $$$$.
What “top opening” are you referring too? Is this something more than
a top vent? The usual front loading burnout oven will allow you to
elevate the flask with some sort of catch tray beneath it. For
elevation I use 1/2" kiln posts and a stainless steel screen to hold
the flask. This screen is a trivet used for enameling. On the kiln
floor beneath the flask I use a piece of aluminum foil to catch the
melted wax. After all the wax has melted, around 300 degrees, power
to the kiln is interrupted, the door opened, and the foil removed.
Power right back on. Removing that melted wax prevents it from
burning up. That burning residue creates the majority of those nasty
fumes. Also, without the fumes the kiln stays very clean. The flask
is never removed using the elevation method.
I’m not sure why anyone would give you that advice. I don’t think
it’s necessary to melt the wax out of your flasks and then try to
remove the molten wax before continuing the burnout. I’ve burnt out
literally thousands of flasks over the years and have never done
that. Any problem I have had with a kiln was never related to wax.
I do put my flasks sprue side down on top of ceramic tile that are
made for my kiln. The tiles have channels that allow the wax to flow
and provide a little air movement into the flask. After the burnout
cycle is complete and my flasks are at casting temperature I like to
flip the flasks over, with the sprue side up, and let them sit like
that for at least 30 minutes in aneffort to allow gases to escape.
That said, some people like to use dewaxers to steam out the flasks
prior to burnout. My feeling is that all that does is cut down on
the wax smoke, but it doesn’t improve your castings. So I guess the
only reason I would do what has been suggested is if you don’t have
your kiln properly ventilated outside, but I don’t think it will
appreciably prolong the life of your kiln…plus it’s a pain in the
###.
In electric kilns the elements develop a protective oxide layer when
heated that keeps the element from evaporating away. The carbon from
the wax fumes will reduce the oxide and allow some of the element to
go away. Do this enough and the element breaks. That said it takes a
long time for this type of damage to ruin an element. The second
reason is less wax fumes in the air so a greener burnout which is not
a bad thing.
Just a question about burnout, I was told that the wax fumes would
shorten the life of the elements.
I bought my kiln in 1982, and I am still on my first set of
elements. Has anyone had to replace theirs ever? I have elements that
are about 2mm in diameter the kiln is rated to 1000 deg C, and I go
to 720 deg C for casting and occasionally to 810 deg C for heat
treatment. It has had a fair bit of wax fumed out through it.
In order not to void the warranty on the new kiln, I will have to
follow their instructions about dewaxing using the wax tray.
That seems like an odd requirement to me. I couldn’t do it because I
always burnout overnight with a programmable kiln. You might look at
some different manufactures, I don’t think Ney has that warranty
requirement and I like their controllers.
I don’t know about the wax fumes, but overheating the investment can
do major damage…it releases sulfides which attack the iron in the
elements/sensors. I once worked for a jeweler who didn’t callibrate
his kiln and just heated it until the flasks were bright red and he
couldn’t understand why he had to replace two temp sensors in short
order or why the neighbors were complaining of noxious fumes!
Just a question about burnout, I was told that the wax fumes would
shorten the life of the elements.
I bought my kiln in 1982, and I am still on my first set of
elements. Has anyone had to replace theirs ever? I have elements
that are about 2mm in diameter the kiln is rated to 1000 deg C, and
I go to 720 deg C for casting and occasionally to 810 deg C for
heat treatment. It has had a fair bit of wax fumed out through it.
I wondered if this was a casting myth.
Not so much a myth as a little bit of an over abundance of caution.
Most folks never run their kiln at or near max temperature if it is
used for burnout. I think these concerns are more applicable to
higher temperatures and or daily use as a burnout furnace. I have
never burned out a set of elements yet either. I have broken them but
never burned a set out.