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Directionality of Burnout Oven


#1

I have a smallish NeyCraft burnout oven. A new ProCraft vacuum
caster has recently arrived and I foolishly bought flasks without
measuring the inside dimensions of the NeyCraft. I now have flasks
that are larger than the oven UNLESS the oven was turned on its side.

We’ve talked it through and the only possible problem we can see is
the fact that the some of the ventilation might be blocked but that
might be solved with some fire bricks.

Has anyone else operated their oven in any other configuration other
than standing on its own legs? Is this incredibly stupid or should
work but will feel wrong?

Thank you again to the Orchid community. You’ve been an incredible
amount of help to me as I set up my studio.

Catherine Keegan
Albion, CA


#2

Hi Karen, It may not be a good idea to turn the oven on it’s side as
the air flow… ( there should be a top hole and a hole on the door to
allow the fumes to escape) will be in the wrong position. Most Neycraft
small ovens have elements that are molded into the insulation and
drilling a new hole will probably go right through the heating
elements. If the problem is the flasks, since they are new,
return/exchange the flasks for something shorter, since height is the
problem. If they are perforated flasks , please look at this page on
my website http://www.racecarjewelry.com/page03.html and you will see
my old system and how we setup standard flasks for vacuum casting . If
you have any questions, please contact me off list and I could help
you out with casting ideas and Daniel Grandi
http://www.racecarjewelry.com We do casting /finishing in gold,
silver, brass/bronze and pewter for the trade


#3

Hey Katherine,

Bummer of a problem! I have a suggestion. Set up a simple steam
evacuation system. (we can talk about this in open studio, or you can
email me directly) If you use steam first to evacuate your wax, then
put your flask in the kiln, with nearly all the wax removed, you can
lay the flask on it’s side and burnout can proceed smoothly. Just
make sure you set the flask up on small blocks so you can reach
around it with your tongs.

Susan

Susan Wood-Onstad, Goldsmith
P.O.Box 1314
Mendocino, CA 95460
(707) 964-0389
@onstad

Jewelry Department Coordinator
Mendocino Art Center
P.O.Box 765
Mendocino, CA 95460
(707) 937-5818
www.mendocinoartcenter.org


#4

Catherine hello!

What you are proposing sounds OK from the outset. The only problem I
can think of is the configuration of the coiled elements in the side
walls. Now, you will have elements, above and below! The unit was not
designed, anticipating this curve ball. The wall below (in your
thinking, the floor!) may be an unforeseen problem in the short term.
Maybe no problem at all. In this case I would talk to the pros. Call
the supplier you got the unit from and have them give you a referral
to the manufacturer and speak with their technical department. Most
manufacturers have pretty savvy gear heads for us to quiz with our
equipment parameters of use. You sure have a new one! Good luck!

Tim


#5

Hi Catherine,

We are an authorized Ney/Neytech/Degusa Ney repair
center/distributor. So I thought I might be able to help.

The simple answer is no don’t do it.

First, it would be best to simply return the flasks and get a size
that fits into your Ney oven. If for some reason you are unable to
return them or don’t want to. Then a new larger oven is the way to go.
If you can’t return them I suggest using a different vendor from here
on out. In business price is always a consideration but so are many
other factors. The cheapest price is not always the best solution.

Setting your oven on its side will create some very costly problems
for you. First, the heating element (the actual wire) is imbedded in
the two sides and the back of the muffle (chamber). This wire is very
susceptible to corrosion and break down from the acids in the wax when
being burned out. If you do wax injection and have ever had your
injector temperature get too hot and when you open the lid you smell
a very strong odor that burns your nose, this is the acid forming from
the wax beginning to burn. There are no elements on the bottom portion
of the muffle because the wax can leak down into the muffle fiber and
would attack the element. This is another reason the element is
embedded in the muffle on the sides. The muffle fiber helps to
insulate the element from the acids formed during burnout. By the way
if your oven does get some wax melted into the bottom of the muffle it
is a good idea to run an empty oven through a burnout or bring it to
1300 Deg F for a couple of hours to burn it out of the muffle. This
wax will not completely burn out when the wax tray is shielding it
form the heat during a burnout. This wax in the muffle will also
eventually wick it’s way up to the element if it is not eliminated.
It flows like solder, toward the source of heat.

The element is one long wire. So when it is broken the whole muffle
needs to be replaced. The suggested list for a new muffle is anywhere
from about $200 to $400 depending on the type of oven you have. Let me
also clarify that the acid from the burnout does not instantly destroy
the element wire nor does it by itself break the wire. What happens is
the acid starts to eat away at the wire. This creates thin spots on
the element that then have a greater resistance than the wire should
have, which when power is applied will create a hot spot on the wire.
As this hot spot gets hotter it will eventually get to the point of
melting the wire. There is one other possibility with the hot spot.
Every time it is heated and cooled it will harden and become more
brittle. If it doesn’t melt first it will become so brittle that it
breaks.

Another problem you will have is as you mentioned the venting. Proper
air circulation inside the oven during a burnout is needed for the wax
to burn. Anything that can burn needs an oxidizer. Without it, it
cannot burn. That’s why your torch has to have oxygen and the space
shuttle needs to have oxygen tanks for it’s engines, there are no
oxidizers in space. You may say but I can light my torch with just the
gas on. Sure, because you have oxygen in the air that is allowing it
to burn. So back to the oven ventilation. Initially the oven will have
some oxygen in it when the burnout starts. But as the oxygen is used
up in the burning of the organics (Wax, Plastic, …) there needs to
be more fresh air flowing into the oven. So the ovens are purposely
not air tight. They have been designed to allow sufficient amount of
air into them for the burnout but not too much so the oven is unable
to reach and maintain the desired temp.

By placing the oven on it’s side you will be defeating the
ventilation that has been designed into the oven. Remember that hot
air rises. That’s why the air vent is always on the top. This allows
the heat to rise and escape and colder air to enter. Then you might
say well let’s just add another hole in the side which would become
the new top. This won’t work because remember the heating element is
in that side. In addition you would need to make sure that the air
flow you are trying to create would come in and reach all areas of the
oven. Without it there will be pockets of oxygen poor air that will
not allow a complete burnout.

Now we get back to the fact that the element would be on the new
bottom of the furnace. This would create a very hot spot on your
flask. Which could and more than likely will cause the investment to
crack. One of the reasons for a burnout cycle taking so many hours is
that the investment being full of moisture cannot handle being heated
rapidly without cracking and breaking apart. The other problem is
what I stated earlier with the fact that the element can’t withstand
the acids created from the burnout. You could not put a tray down on
the bottom to catch the wax because the tray would block enough of the
heat being generated from the element and would overheat it which
would melt the element and you would need a new muffle.

Then we get into the heating of the flasks. For a good burnout the
flask(s) need to be heated evenly. If the flasks are not heated evenly
there will be cold areas where the wax will not burnout completely. If
you were to get the wax to burn out completely you would still have
cold spots and hot spots on the flasks. This would create metal flow
problems. The reason you don’t just burnout the wax and let the flask
cool then pour the metal in is that the metal would chill too fast
when coming in contact with the cold investment. This is what would
happen with your flasks. Although you would get some areas to fill
that were the proper temp the cold areas would not fill because the
metal would chill. Remember that we are melting the metal but not
heating it too much more than the solidification point. If you were
to heat the metal way over the solidification point you would create
other problems with your metal. Such as losing some of the ingredients
of the alloy (which changes the quality and karat value), firescale
and many more.

There are other reasons why these ovens and for that matter all
equipment should be used as the manufacturer designed them. Sometimes
equipment can be used a little different from the designed use but as
a rule any major differences would result in very expensive lessons.

– Ken Kotoski MPG Repair www.mpgrepair.com

We repair the tools jewelers use.


#6

Not a good Idea to lay the flask on it’s side after steam dewaxing as
there will still be some wax trapped in small areas that will boil
and cause surface problems in those areas. It may work occasionaly.

Daniel Grandi


#7
 The element is one long wire. So when it is broken the whole
muffle needs to be replaced. The suggested list for a new muffle is
anywhere 

I have an oven in which the elements can be replaced. About a $40
part. Isn’t this better design?

Roy


#8
    I have a smallish NeyCraft burnout oven.  A new ProCraft vacuum
caster has recently arrived and I foolishly bought flasks without
measuring the inside dimensions of the NeyCraft.  I now have flasks
that are larger than the oven UNLESS the oven was turned on its
side. 

I don’t wish to be obtuse, but why don’t you just set the flasks in
sideways? Reminds me of the guys installing the light bulbs by
turning the ladder round and round. I know that many people advise to
do burnout with the sprue on the bottom, but I think that it really
makes little, if any difference. Either way, combustion of the wax will
take place and the further oxidation of any remaining carbon will take
place at burnout temperatures. Some have said that peculiar gases for
on the flask cavities, but I find this hard to believe considering the
porosity of the investment, especially if vacuum
casting is being done. Just my opinion.


#9

I have run various kilns in non-standard orientations (like on their
sides). Things to watch out for - heating elements falling out of
their grooves, eveness of heating of the flask, ventilation (like you
said), and most importantly, you need a large enough space between
the new bottom side of the kiln and the table it sits on to prevent
cathing the tabe on fire. Think of the table top as an extra layer of
insulation, allowing the kiln surface (and thus, the table surface)
temperature to rise. Have you thought of just burning out the flasks on
their sides?

Looking forward:
Alan Shinn

Experience the
beginnings of microscopy.
Make your own replica
of one of Antony van Leeuwenhoek’s microscopes.
visit http://www.sirius.com/~alshinn/


#10

It makes a huge difference. If you let the wax run out the sprue
opening the majority of the wax runs out at low temperature. But if
you lay it on its side the cavities on the bottom half of the mold
will not drain then the wax sits in the mold and boils which causes
deterioration of the mold cavity and results in terrible surface
finish. It will also allow more wax to seep into the investment
deeper which will lengthen the burnout time significantly. Two to
three times longer! In short don’t do it unless you want crappy
castings.

Jim
James Binnion Metal Arts


@James_Binnion
Member of the Better Business Bureau


#11
I don't wish to be obtuse, but why don't you just set the flasks in
sideways?

Red Rodder, I had that problem once when I used a steel mini beer
barrel to cast a statuette. First I had to weld up a flask holder with
detachable handle so I could get the thing into and out of the burnout
oven, then I had to dewax by setting the flask into the kitchen oven
over a pan to catch the drippings.

After dewaxing it was simple to transter using the flask holder, lay
it sideways into the burnout oven, take my wife out to lunch, a movie,
then to dinner while it was burning out (yes there was a price to pay
but it took that long to air out the house) then come home and cast.

The thing was so big I had to put it in to a sand pit in the yard,
heating the metal in a centrifugal propane foundry and gravity pouring,
but it worked, with just one little filling defect where a sprue
slipped off.

Geo.


#12

Hi Roy, Having an exposed element makes changing them easier and less
expensive. The elements are usually heavier duty than embedded
elements. This is because they are directly exposed to the acids
formed during burnout. Most of the time you will find this type of
element is in ovens using firebrick or ceramic plates for insulation
rather than ceramic fiber. The ceramic fiber is to fragile to be used
with exposed elements. It would not withstand the removal and
insertion of new elements. There are advantages to both types.

The ceramic fiber type is much lighter and insulates better than the
firebrick and ceramic plate ovens. While the firebrick and ceramic
plate ovens make changing elements easy and less expensive they also
usually have multiple elements so if one element fails in a burnout
the whole oven won’t completely cool possibly damaging the invested
flasks. Although it will probably be impossible to reach the top
burnout temps. they could possibly be able to reach around 1000 Deg
F, which if the flasks were left in long enough would allow a good
burnout. This type of burnout is used for stone in place casting.
where the oven doesn’t get above 1000 Deg F. Firebrick and ceramic
plate ovens are very heavy so they need to be supported better. Some
ceramic plate units will use ceramic fiber behind the plates for
insulation. This gives a better insulating factor and makes the oven
lighter weight.

The elements in a ceramic fiber oven aren’t directly exposed to the
acids so the elements can last longer than exposed element ovens. As
with all things this will depend on use and care. With gas ovens many
of the problems found in electric kilns are not present.
Ken Kotoski
MPG Repair
http://www.mpgrepair.com
We repair the tools jewelers use.


#13

The problem with setting the flasks on their sides is that you will
not get a complete burnout and if in fact you are vac. casting you
will not get a vacuum to pull through the investment. Centrifugal
casting requires that the investment not be impeded as well so the air
can move through the investment and the metal can fill the cavity. In
this case the metal will force some of the air through the investment.

What happens is the wax melts first. When it melts a small amount
will get absorbed into the porous investment (if standing up with the
sprue opening down). This small amount of wax that is absorbed
(usually no more than a 1/4" deep into the investment or for steam
dewaxed flasks about 1/8" deep) will be able to be burned out
including any residue left in the cavity at 1350 Deg F if the flask is
kept in for the correct amount of time at this temp. However setting
the flask on it’s side will not allow the wax to drain out completely
and will pool inside the cavity allowing more wax to penetrate the
investment. The deeper it goes the harder it will be to burn it out.

First the pooled wax will have to burned out which does not happen
instantly. It takes time to burn something. Therefore a normal burnout
could not be used and instead the high temp would need to be held
for
a very long time (possibly days) in order to eliminate the pool of wax
and burn out the some of the wax that has penetrated the investment.
Although the investment is porous it is not as though air will move
through it at will. It has to be forced through it.

So without a way to force more air into the investment for combustion
the wax that has penetrated deep into it will not burn out. Therefore
if you were to wait for the pool of wax to completely burnout and try
to cast without getting all the wax burned out of the investment you
won’t get a good fill and complete fill. You will get this because the
air in the cavity will be trapped and will not be able to penetrate
the investment due to the wax blocking it. In addition the hot metal
will vaporize a small portion of the wax residue left in the
investment causing gas porosity in the castings.

Ken Kotoski
MPG Repair
http://www.mpgrepair.com
We repair the tools jewelers use.


#14
The problem with setting the flasks on their sides is that you will
not get a complete burnout and if in fact you are vac. casting you
will not get a vacuum to pull through the investment.

In fact, I usually, though not always burn out with the flask on
their sides. I might point out that I do 2-3 castings a week, rarely
using more than an ounce or so of gold. Using small flasks has shown
me that complete combustion has taken place. Using these small flasks
has enabled me to get a rush job burned out in an hour to an hour and
a half. Vacuum draw works fine. I find no residue of carbon in the
investment. Occaisionally, I use larger flasks, and I have learned
through experience, not just by someone telling me what is and what
isn’t practical that the larger flasks need to be treated more
delicately. I don’t advocate fast burnout or sideways burnout on a
regular basis, only to get the job done the equipment at hand with the
time available. When I do castings like this, I am subjecting my work
to more abuse than I would like. Some of us do repairs with a Hoke and
some of us require a laser.

Let’s look at what happens when burnout takes place. As the flask
warms, the residual water may begin to boil, forcing some of the
softer waxes out. This boiling can in fact cause damage to the
investment walls if too violent, especially if harder waxes are
present. I have watched some of the carving waxes carrying out small
chunks of investment at about this stage. Steam dewaxing, although I
haven’t done it, I trust, will eliminate this phase of difficulty
because there is no boiling action taking place inside the flask or
more importantly, inside the walls of investment… Although I wonder
if carving waxes can be eliminated this way. With the water
evaporated, the flask now begins a slightly quicker warming, as there
is no vaporising water to cool things down. The wax liquifies to a
very thin consistency and usually combusts as there is plenty of
oxygen in the atmosphere. Some of the wax is absorbed into the
investment. Most of the burning wax becomes CO, CO2 and H2O. Prior to
combustion, some of the wax is vaporizes and escapes the oven in the
form of fumes. The liquid wax cools to flask just as the water used
to, but at much higher temperatures. This burning can be compared to a
candle burning. Any carbon left in the flask is soot. The same soot
that goes by the name of candle black. If the wax has been brought to a
boil, it can cause the same damage as the boiling water. By bringing
temperature up in a controled fashion, this violence may be eliminated.
Brunging the flask temperature over 1,350 degrees F will quickly cause
the carbon to oxidize and form CO or CO2. This may take a while
longer for larger flasks as investment is a good insulator, but being
heated from the walls of an oven the center of the flask will warm in
fairly short order. As I write this the realization just came to me
that there is probably better air circulation providing better
combustion while the flask is on it’s side. That is my experience.
Think of the times that we have burned out insects or pieces of wood
or other forms of organics other than bone or shell. This doesn’t
require an extreme amount of time, just an extreme temperature with
plenty of oxygen.

You may note that there are three distinct phases in the above
burnout description. Water elimination, wax elimination and carbon
elimination.

. When I first heard of dewaxing many years ago, it was described as
a method to eliminate the buildup of wax fumes in poorly ventilated
shops not a method to produce a better casting, just a method to
eliminate most of the fumes.

I love this forum. I learn something new every day. This post has been
way too windy, and I apologize.

Bruce