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Lost wax casting, reducing burnout time


#1

I teach metals at a community college that has an ancient gas kiln.
This kiln requires constant monitoring during its full 7-8 hour
burnout cycle. Before, my classes had been in the evening, so
someone (usually me) came early to tend the kiln. Next year, the
class will be offered on Friday mornings.

I’d like to teach some lost wax casting, but without having to get
there at 3a.m. to tend the kiln. Does anyone know of any possible way
to reduce the burnout time to 2 or 3 hours? (I’ve tried for years to
get the college to buy a programmable kiln, but the answer is always
no.)Thanks for your help!

Charity Hall


#2

Dear Charity,

Here is one solution I have used for many years.

I too had an old gas oven that needed someone to monitor it as long
as it was operating. It was very inconsistent, especially in the
winter months. Remember that city gas is designed for heating
furnaces not burn out ovens.

With a large cast it was always late in the class scheduling to cram
it all in. Many time we had to cast after the class was over and
another one starting. Many times we have over twenty flasks to cast
in one class. Each student may cast as many as two flasks per class
with a casting class lasting fourteen to sixteen sessions. Casting as
much as possible is an absolute must to start to learn the casting
process.

I replaced it with a 220 volt kiln with a regular rheostat NOT a
programmable one. The dry electrical heat is also, in my opinion, a
cleaner burnout. I also have a small Neycraft one for smaller loads.

What you must find is the dial setting that reached your peak burn
out temperature. I ramp the oven up to 1350 f for the peak
temperature. The control dial on this oven is set at 3.5. The oven
will slowly climb to that temperature overnight. It operates like a
room getting warmer and staying at a set temperature. By setting the
oven on the pre set number it does climb gradually which is what you
want. This process goes through the peak burnout cycle successfully.
I have done this now for over thirty years. Small and large loads
work successfully this way.

I do have a code steel and concrete work bench that is vented so I
do not worry about anything going wrong. If the oven malfunctions, it
would be a wire melting, which shuts everything down. I’ve had this
happen only twice in over forty one years of casting.

When you arrive for class all you have to do is turn the oven down
and wait for your casting temperatures. Time wise this is ideal
because all the burn out happens while you are gone. By setting the
oven to climb to peak temperature, you don’t have to worry about the
programmable control not working properly.

If you go to the Southeast Technical College Jewelry page you will
see my current ovens and casting set up. The spin caster is over
twenty five years old and still works like a champ. A bit beat up
mind you, but a hearty machine.

http://www.ganoksin.com/gnkurl/1va

In fact our casting machine is one of the Lucas Casting machines
#750 linked on Orchid. An older unit, but built to last.

Best regards,

Todd Hawkinson
Southeast Technical College
www.southeastmn.edu/jewelry


#3

Hi Charity A steam de-waxed, store bought or homemade, will help
enourmously. People have built them from pressure cookers…,

Take care, andy


#4

Charity,

This suggestion may seem a bit radical but it was originally
suggested to me by the retired Director of Research at Ransom and
Randolf and I have been using this method in my classes for a number
of years:

First, keep your invested flask saturated with water, don’t let it
partially dry out. Remember that investment hardens by a chemical
reaction that proceeds when the flask is submerged in water.

Next, turn on your burnout kiln or oven and raise its temperature to
1350 F. Find the manual setting that will hold that final burnout
temperature or set your controller to hold 1350 F. Put the moist but
hardened invested flask directly into the HOT oven! Don’t worry, a
properly invested won’t explode or crack.

The moisture in the investment will hold the invested flask below or
at 212 F, the boiling point of.water for a half hour or so depending
on the size of your flask or number of flasks. Then the temperature
of the flask will start to rise toward the final burnout temperature
of the oven which can take from one to several hours depending on the
thermal mass of the flask or flasks in your oven. The flasks will
become a dull red when they reach the final temperature. Hold at 1350
F for a while and then reduce to your final casting temperature.

As mentioned before, I have been using this approach for a number of
years in my classes. All the details and experimental data is
described in my book “Lost-Wax Casting: Old, New, and Inexpensive
Methods.” Get in touch with me if any of this description is not
clear.

Fred

Fred R. Sias, Jr.
Woodsmere Press


#5

I used to serve the role of casting officer in the jewellery making
club I belonged to. Our usual procedure was to invest our flasks a
couple of days before casting. They can easily keep for more than a
week if you leave the plastic bag. However if we were casting within
3 days we left the flasks out on a shelf to dry out.We use fairly
small flasks usually about 40mm diameter in a centrifugal caster. We
started burnout when casting at about 8:30 in the morning by taking
it up to 200 (all temperatures in degrees Celsius) holding for 30
minutes then up to 400 until most of the wax had burnt out, then up
to 500 and holding for 30 minutes and finally 650 and hold for an
hour. We then set the thermostat back to 450 and started casting as
soon as the temperature had dropped to that point. This gave us
around a 4 hour burnout cycle so we could start casting after an
early lunch.

The point is that you can run a much faster burnout on small flasks
that the larger ones I now use in my vacuum casting setup.

All the best
Jenny


#6
A steam de-waxed, store bought or homemade, will help enourmously.
People have built them from pressure cookers..., 

Since the casting waxes melt well under the boiling point of water,
you don’t even need a pressure cooker. You DO need an old pot which
you won’t want to use for food again, as it will get nicely and
messily coated with wax. Put some water in the bottom, then
something, perhaps an old veggie steamer, down next so you can
support the flasks up out of the water. Put the cover on the pot,
and turn on the stove, letting the water boil, filling the pot with
good hot steam. Come back in fifteen minutes or so, and they’ll be
dewaxed nicely. A pressure cooker can speed it up, and can remove the
higher melting carving waxes too, but for normal injection waxes, is
not needed. Commercial steam dewaxers are not pressurized, or at
least, the ones I’ve seen and/or used are not.

Peter Rowe


#7

Thank you, Todd. Looks like you have a great program/studio setup.
Your solution sounds great. Although last year, I had asked for a
Neycraft as an alternative if the college could not/would not buy the
programmable kiln. Unfortunately, that request was also denied. But
that was last year. I’ll try again and see what happens.


#8

check out the rice steamers at your local discount store. I bought
one for around 20bucks and it works great. Has a water reservoir and
a plastic grate that sets just above it. The wax melts and drips down
to the water reservoir.The water for the steam comes from a different
reservoir than where the wax drips. works like a charm.


#9

Wow. This might work as we have an old dewaxer somewhere. So just to
clarify…if I dewax with a steam dewaxer, can I take those flasks
and then put them directly into a kiln already heated to 1350, then
hold that until the flasks glows red, then lower to casting
temperature and cast?

Many thanks,
Charity


#10

I have a small steamer designed for heating and frothing milk. I put
a plastic extension tube over the steel nozzle and use a pair of
self-grip tweezers to stop my fingers getting scalded and away it
goes. Catch the wax in a shallow tray and can still boil milk if I
need to take a drink.

Nick Royall


#11

Dear Charity,

You might approach this concern with three strategies.

  1. SAFETY Gas is much more dangerous than electric. If something goes
    wrong you have gas filling the room and building. Boom…With an
    electric problem, a wire will most likely burn out and the burnout
    process just stops. I have used Neycraft ovens since they were
    introduced and have never had a problem with them. I have not used
    the programmable ones. OSHA or someone from your facilities may have
    a say in this area.

  2. Do you have an advisory group that could make any recommendations?
    Most times colleges do not listen much to faculty, but will listen to
    someone outside of the institution.

  3. Sometimes a tool supplies has some returned items or could make a
    donation to your program. Great press for them, and great for
    attracting student to buy their supplies.

Good luck and best regards,

Todd Hawkinson
Southeast Technical College
www.southeastmn.edu/jewelry


#12

Charity,

That should work fine. Steam dewaxing saturates the investment and
keeps it from heating up too fast. However, when put into a 1350
kiln without steam dewaxing, the wax burns to co2 and there is very
little smell. Try it. You need to adjust time depending on size and
number of flasks. Remember that chalky white sprue opening is
indication that burnout is done.

Fred


#13
Wow. This might work as we have an old dewaxer somewhere. So just
to clarify...if I dewax with a steam dewaxer, can I take those
flasks and then put them directly into a kiln already heated to
1350, then hold that until the flasks glows red, then lower to
casting temperature and cast? 

Small flasks only! if you try this with a larger flask it will
likely cause problems. You are better off ramping up to temperature
rather than going straight into a 1350 F kiln. All of these rapid
burnout “tricks” will produce less than optimal castings (reduced
surface quality and more gas porosity) but sometimes you just have
to do what you must to get the job done.

James Binnion
James Binnion Metal Arts


#14
All of these rapid burnout "tricks" will produce less than optimal
castings (reduced surface quality and more gas porosity) but
sometimes you just have to do what you must to get the job done." 

Jim is right here. We’ve had to do do “Jiffy Burns” in the distant
past for a particular was carver we knew who would procrastinate
until it was too late. Every time there was an issue with the
quality. We have a rule now. No compromises.

Have fun and make lot of jewelry.
Jo Haemer
www.timothywgreen.com


#15

Investment is basicly made out of refractory and binder materials.
Gypsum is used as a binder and crystobalite, quartz, magnesium oxide
as refractory with wetting agents and surfactants.

All these components are standing in close relation to eachother and
carefull calculated and tested by manufacturers for best results.
They know exactly how investment behaves and the result of leaving
the safe zone of their product.

If you realy like to leave that safe window, you better ask the
manufacturer in which direction you walk into -blindfolded- by
shortcutting their procedure.

Different company’s have different formula, different patents an
different uses for their investment product.

Yes, I use shortcuts too but for more then 90% procent I use the
rules of the manufacturer. I can always give them a call if it go’s
wrong. By sticking to their recommendations they can advice me in a
proper way.

It works well for 100 times but it turns bad when you’re in a hurry
and then you’re in serious trouble due to lack of time. If you have to
tell you customer that it turned out bad and her/his wax just
vaporated into nothing because you used a shortcut… you’re in a
ugly position brother!

If you do need to use an other burnout cycle, then inform your
customer of what can happen. Keep in mind that if you follow the rules
things can go wrong aswell and that’s already painful enough to
explain in my opinion. When the casting is only for your benefit,
then deal with the shortcut as it comes.

Enjoy and have fun
Pedro