I am looking for on steam dewaxers. I have spoken with
several jewelers who don’t see any use for them, and consider them a
complete waste of money. Someone has convinced my employer (who is
broke as broke can be) that he must have one. What is the general
opinion of the jewelers out there? I personally don’t think we need
it. If you do, please convince me.
LaVerne
If you are mostly doing carving wax, there may be little use for one
because most carving wax does not steam out…but if you are doing
injection wax models, then yes, it is a good thing to have…the
main reason being that you reduce the amount of fumes is reduced by
something like 90%…so if you are in a building where the fumes can
travel to other shops, or if anyone is sensitive to the fumes, it’s a
must. I used to get lung issues (asthmatic bronchitus), and while I
don’t seem to have a problem with it now, I don’t want to risk
irritating my lungs with burning wax fumes.
I’m also working with filigree, and I think it gives me a better
burnout and the cleanup is easy…once the chamber cools, the wax
forms a thin sheet on top of the water you can just rip out and
throw away.
Jeanne
jeannius.com
creativecabs.com
I think it depends on how much casting you are doing at one time.
Ask yourself if the current burnout is producing an unacceptable
level of smoke. I have a steam dewaxer but I do not use it most of
the time. This is because most of the time I am only burning out six
or fewer smaller flasks. I burnout overnight, so nobody is around
when the fumes are stinking the place up. But then I also cast in a
room that is separate from the rest of my shop, so maybe I can
tolerate a little more smoke. It takes more time to do the dewaxing
and you should move the flasks directly into a preheated kiln before
they cool. What I do with just a few flasks and no steam dewaxing is
have the kiln timed to start the burnout at midnight. If I had
steamed them I would need to have the kiln programed to be hot much
longer overnight or steam early in the morning and then burnout all
day and cast in the afternoon.
Bigger flasks need a longer burnout anyway and when I have a lot of
casting I will use the steam dewaxer. I have not noticed much
quality difference between steamed or not. 10 or more 4 inch flasks
are going to make a lot of smoke when they burn out. Better to put
them in the steamer.
You can steam dewax in a large stock pot on a stove or hotplate. But
if you have few enough flasks to do it that way, it probably is not
worth the bother.
DO NOT STEAM OUT CARVING WAX!!! It won’t work and will damage your
investment.
Steam dewaxers can make for improved quality in your castings, but
they can also screw up your castings if you don’t use them properly.
The only real reason I would put one into your process is if you have
air quality issues you need to address. The biggest improvement they
make is in reducing the amount of wax that is burned.
James Binnion
James Binnion Metal Arts
Steam dewaxers can make for improved quality in your castings, but they can also screw up your castings if you don't use them properly.
How? Would you elaborate, please? Anything I can learn can only help
me get better castings.
Kathy Johnson
Feathered Gems Jewelry
Steam dewaxers can make for improved quality in your castings, but
they can also screw up your castings if you don’t use them
properly.
How? Would you elaborate, please? Anything I can learn can only help me get better castings.
If you steam dewax your flasks should not be allowed to cool or the
wax residue will be absorbed in the investment and then cause surface
damage when it is heated later on. So you should move your flasks
right from the hot steamer to a kiln that is a little bit hotter than
the boiling temperature of water. 250 to 300 degrees F is about right
for the kiln. In my program we hold at this temp for several hours
until the real burnout starts. This is a matter of timing, as the
length of this stage of the cycle is adjusted so that the final
temperature is right when I plan to do the casting, usually the next
morning.
Trying to steam carving wax will not work because carving wax melts
at higher temperatures. It burns out just fine but steaming it will
screw it all up.
You might have problems if you try to steam your flasks before the
investment has had enough set up time. This is also true if you start
the burnout too soon. Let your investment set up at least an hour
after it gets solid. Two hours or more is better.
Steam dewaxers can make for improved quality in your castings, but
they can also screw up your castings if you don’t use them
properly.
How? Would you elaborate, please? Anything I can learn can only help me get better castings.
First off steam dewaxers are meant for use with injection wax. Any
other type of wax can cause problems ranging from minor to severe.
One of the problems with steam dewaxers that caused us grief till we
figured it out is that you can melt the wax in the peripheral areas
of the flask before the center sprue melts. When you do this there
is a rather significant pressure increase in the mold cavity from the
thermal expansion of the wax. This pressure can cause local mold
surface breakdown and you end up with defects ranging from rough
surfaces to finning and spalling of the mold face depending on how
severe the problem is… This can be made worse if you use a sprue wax
that has a slightly higher melting temperature than the injection wax
of the patterns. How bad the problem is will depend on many factors:
flask diameter, pattern size, position in the flask, how powerful
your steamer is etc. To solve this we put a temperature controller on
the steam chamber and kept the temperature at about 180 F this slowed
down the rate of rise in the chamber and the problems we were having
went away. We also tried things like using a modified soldering iron
to melt out the center sprue before placing the flask in the dewaxer
but this results in too much handling of the flask and more potential
to damage the flask. To see if you are having this kind of issue look
at the surfaces of your castings before removing them from the sprue.
If they are rougher out at the periphery of the flask then this may
be the cause. If you are doing small flasks you may not see this as
often or at all. We were seeing it in 4"x9" flasks. of which we were
casting 20-40 a day.
Jim
James Binnion
James Binnion Metal Arts
If you steam dewax your flasks should not be allowed to cool or the wax residue will be absorbed in the investment and then cause surface damage when it is heated later on
After I invest, I wait 2 hours and put the flasks in the dewaxer turn
it on and go home, I put the flasks in a cold kiln the next morning.
If I can invest and dewax by the time my store closes, I put flasks
in the kiln and use the delay start set to start at 3 a.m. I have
not been experiencing surface damage.
If I invest and wait 2 hours and then steam dewax I have no problems.
I have a store bought dewaxer now, I used to use a pressure cooker
used for canning, I could fit 9 3"x7" flasks, leaving the vent open
and heating till steam was hissing from the vent. Flasks were then
put in a cold kiln and I did a 8 hour burnout. This worked great and
I did this for 12 years.
Richard Hart
After I invest, I wait 2 hours and put the flasks in the dewaxer turn it on and go home, I put the flasks in a cold kiln the next morning.
Another jeweler’s myth bites the dust! I think I read the bit about
not letting the flasks cool in one of the manuals that came with the
equipment. Is there something about jeweler’s mindsets that makes us
prone to perpetuating practices and superstitions about how things
must be done that have no basis in practical reality?
Another jeweler's myth bites the dust! I think I read the bit about not letting the flasks cool in one of the manuals that came with the equipment. Is there something about jeweler's mindsets that makes us prone to perpetuating practices and superstitions about how things must be done that have no basis in practical reality
Ah,
now the thing about steam dewaxing is that it doesnt drive off the
water of crystallisation as the temperature is too low. Gypsum will
turn to a hemihydrate at 115deg c but this is reversible and the
water vapour will ensure that this happens. When you do a burn out
the plaster converts to an anhydrous phase known as dead burnt
gypsum {because it had a different structure to anhydrite or
alabaster} that cannot reform to ordinary gypsum plaster. letting
this cool and absorb moisture will cause a swelling of the investment
which will ruin it after a fairly short time. Letting it cool to just
above 100 deg c is OK for leaving overnight but longer than that
wouldnt be recommended. The shrinkage caused by permanent loss of
water is matched by the expansion of the quartz as it changes phase
to high quartz, hence the mix proportions of gypsum to quartz flour
in investment plaster. Plaster for platinum casting uses more quartz
and zirconia flour to minimise the breakdown of the gypsum to calcium
oxide and sulfur which is noticable when you overheat your flasks by
the smell and discolouration.
The full chemistry behind all of this was only correctly worked
proved about 9 years ago despite the same mixture for investment
plaster being used for a couple of hundred years. I have done
analysis of ancient floor plasters for archaeological purposes and
the modern manufacturers cannot match the original so it was then a
matter of bucket chemistry to work out how it was done. The end
result was quite interesting but not what people supposed when we
started the project for English Heritage. People used to do things
in a way that worked wheras now we tend to do computer simulations
first and then try it out and if it doesnt work fiddle about with the
computer model.
Nick
Hi Nick,
Plaster for platinum casting uses more quartz and zirconia flour to minimise the breakdown of the gypsum to calcium oxide and sulfur which is noticable when you overheat your flasks by the smell and discolouration.
Most of the platinum investments I am familiar with are phosphate
bonded and have no gypsum in them. Because the gypsum breaks down
above 1200-1300 F (depending on how much residual carbon is present
in the investment from burnout) and begins to release the sulfur as
sulfur dioxide gas which is readily absorbed by many molten metals
and is one of the primary sources of gas porosity. This breakdown
also causes rougher surfaces and loss of strength. The phosphate
bonded investment is a royal pain to remove because it is so much
stronger than the gypsum variety. What brands of platinum investment
are gypsum bonded?
Jim
James Binnion
James Binnion Metal Arts