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Burnout options


#1

Let us say that one wants to burn out a flask and does not have a
kiln. What are the alternatives. Can you use a gas grill, a hot
plate, etc., etc.? Please advise.

Marshall


#2

Try a clay flower pot - about 5" diameter opening - line it with
aluminum foil and use it on top of a regular hot plate. Burn out
takes a little less time - but it works fine – I used that system
both for centrifuge and steam casting with good results. The burnout
is complete normally when the sprue opening is white or light - not
showing any dark unburned wax remains.

Regards,
Joe


#3

You can use all of the above and a few other things. Here’s a method
that’s gotten me thru a couple of emergencies. You need: 1) an
electric hot plate without a thermostat (it must be “on” at all
times); the nichrome element type is recommended, not the calrod
type. 2) a terra-cotta flower pot big enough to cover the flask,
allowing about an inch of extra space both vertically and
horizontally; 3) a sheet of heavy-duty aluminum foil big enough to
wrap the inside of the flower pot; 4) a well-ventilated area with a
power supply for the hotplate, and 5) at least 6 hours of your time
for an average 2 x 3-inch flask with, say, a single gent’s ring wax
or an average ladies’ ring or two.

Place the flask on the edge of the hotplate with the sprue-former end
downward. Situate it so the molten wax does not directly contact an
element when it liquefies and flows out. (It’s best to place a little
aluminum foil below the flask opening to catch the bulk of the wax –
wax that sticks to the hotplate can be removed with denatured alcohol
or nail polish remover).

Turn the hotplate on a low setting and leave it uncovered until most
of the wax has been eliminated. Every couple of minutes lift the
flask with tongs and observe to see if the wax is flowing freely,
not boiling out. Adjust temperature if necessary. This process should
take 30 minutes or so on average, but don’t rush the process!

When little or no wax is flowing out, gently increase the temperature
setting and move the flask incrementally toward the center of the
hotplate with your tongs. If the wax starts sputtering and
splattering you’re going too fast and can ruin the mold. Reduce heat
and go back to Go. Allow up to 90 minutes or more to complete moving
the flask to the center of the hotplate, increasing the temperature
to the highest level as you go.

When the flask is at the center of the hotplate, cover it with the
inverted flower pot to create a mini-oven. Burn-out from this point
should require about 4 hours (more for larger flasks, of course).

The advantage of using an electric hotplate instead of an open flame
or barbecue briquets (it’s been done!) is that the investmen is not
carbonized by the flame, so it’s easy to judge when all the wax has
been burned out. All traces of gray will be gone and the investment
will be a uniform chalk-white. It’s usually best to cast immediately
after removing the flask from the heat, but this is a very imprecise
process and experience is the best teacher. Practice with commercial
waxes first, and don’t start with your priceless originals!

Warning: do not use sections of galvanized pipe for flasks.

When heated they can give off poisonous fumes. The best source of
cheap flasks I’ve found is my friendly neighborhood muffler shop.
They have a bin of cut-offs they let me pick through. I have them do
all my muffler work, of course, and send all my friends there.

Good luck!
Rick


#4

making your own furnace is necessary- most gas stoves don’t get up
to the temperatures requireed to remove all water from the
investment. But there are other direct casting alternatives like
shell casting, cuttlebone, delft clay, sand casting. etc…rer


#5
Let us say that one wants to burn out a flask and does not have a
kiln. What are the alternatives. Can you use a gas grill, a hot
plate, etc., etc. Please advise. 

The method described in an old pamphlet on steam casting methods,
suggests taking a suitably sized red clay (terra cotta, I guess)
flower pot, lining it with a layer of furnace tape (this used to be
asbestos, but these days, is other mineral material. Works the same.
You may need to wet it to form it to the inside of the pot), and then
a layer of heavy aluminum foil. Keep the small hole at the bottom of
the pot open. Your flask goes, sprue down, on the kitchen stove
burner (either gas or electric), with the pot over it, set on high.
It will easily reach needed burnout temps this way. I recall being
able to get the flask to a nice low red/orange glow, easily near the
desired 1300F temps. One assumes the use of sufficient stove vent
fans, preferably the type vented to the outside, to handle wax
burnout fumes, and I’d suggest rigging up a steam dewax first, to
minimize fumes. When I did it, decades ago, I also took care that
the flask was off center on the burner, so over the liner under the
burner to catch drips, instead of over the hole often in the center
of such liners. You will want to get the permission of any
significant others who also use your kitchen before doing this.
Alternatively, any small electric hot plate that could equal a
typical stove burner should work as well, and that could be placed
outside or in the garage or something to avoid the ire of fellow
inhabitants. The real key to it all is the “kiln” made of the
insulated flower pot. Don’t know about a gas grill, but if it directs
enough heat up into that pot, don’t know why it wouldn’t work…

HTH
Peter


#6

Marshall, Yes, you can use a hotplate. Get a couple of terra-cotta
flower pots, line one with aluminum foil and place the other inside
it. Place upside down on the hotplate (with the flask underneath of
course)

Jerry in Kodiak


#7

Hi Marshall,

I can’t draw upon direct experience here because I have always used
a kiln for burnout so I looked at some of my books. Tim McCrieght in
"Practical in the form of an enclosure of firebricks heated by a gas
torch against an internal baffle so that the flame doesn’t touch the
flask. I really don’t know how this would work in practical terms.
The problem is that burnout requires fairly precise temperature
control so that the investment is properly dried out, is not
subjected to rapid temperature changes engendering thermal shock and
is given sufficient soak time at a temperature 650-700C (a dull red
heat) to ensure a clean burnout of wax but not exceeding 735C where
the gypsum in the investment starts to break down and then taken down
to 450C for casting. This is a big ask for an improvised kiln.

You would be better off trying, as I did, to buy a second hand kiln
with some form of thermostat to control the temperature. A
programmable ramp controller is nice but you can manage quite well
with a thermostat to manually control your burnout cycle.

If this option is outside your budget It would be better considering
alternative forms of casting such as delft clay or cuttlefish. The
other alternative is send your castings off to a company that
specialises in precious metal casting. I do all my own casting at the
moment but I know send work off if I am under pressure at $5 + metal
each for small patterns (up to 20 grams)

All the best
Jen


#8

I have discovered from others that the older hot plates have a more
direct and hotter transfer of heat than any new hot plates. Go on
eBay, look for hot plates that have the older cloth covered power
cords and exposed element/burner. I found a mint condition one for
20 bucks. But I heard its getting hard to find the older hot plates.
Mine works great, gets plenty hot ifyou use the double insulated
flower pot method. Best of all, as everyone discussed, you can burn
outside since its Easy set up.

Has anyone discovered how to avoid the iPad email glitch that messes
up my writing after I submit a perfectly typed email? Am I the only
one who has this problem?

Rick Powell