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Casting reheating investment molds


#1

our vacuum pump shot craps today, and the molds were in the oven
buring out we do a all night burn out, will they be alright to
reheat?? also how reliable is steam casting?? i.e potato thanks Rick


#2
    our vacuum pump shot craps today, and the molds were in the
oven buring out we do a all night burn out, will they be alright to
reheat?? 

Rick, I understand that you can “Hold” a flask for quite some time
at heat. I know that some years back, I was taking a class at the
local state college, and the instructor mentioned that he would put
a weeks worth of flask in the oven at once and then as a students
class came up, it was ready for them to cast.

For a repair for your vacuum pump, try Graingers. They have a
refrigeration repair pump that is an exact replacement for the vane
pumps is some of the casting machines. They usually have one in
stock in the larger cities. The price is much less than you will
find if you go to Rio or the other tools distributors, and you can
get it quicker.

  also how reliable is steam casting?? i.e potato thanks Rick 

I wouldn’t try it for something I really needed. The flask needs to
be sprued differently . IE many small sprues vs a large one so that
the melt will stay in the sprue button until the steam is applied.
If you have a 1/4" sprue from the button, the melted metal will run
down and cool prior to applying the steam. You need many small,
1/16" or so spures from the button so the surface tension holds all
of the metal in the button until the steam is applied. One more
point, your sprue button needs to be big enough to hold all of the
cast and some for the button, as you use the button to melt the
metal. I guess that this means that if you invested a piece for
vacuum casting, it wouldn’t work for steam casting.

Don


#3

Rick, I won’t comment on reheating flasks cause I don’t do it. Seems
to me you risk cracking etc. I do not mind storing newly poured
flasks overnight in plastic bags then burn out the next day but I
would expect problems reheating after burn out. Sure someone else
out there has more to say on this subject.

Re steam casting…I have done it for many years and had great
success. Doubt if I lose more than one or two out of a hundred. The
problem though is in the preparation. In steam casting, the shape of
the indentation around the sprue hole is different…it is a shallow
concave area usually cut out with a spoon shortly after investing.
That is because the metal is melted in this depression prior to
applying the steam generator to shoot it into the mold. Also, the
spruing is different. Some people use several sprues closely
grouped…either narrow strips of wax or wire around 24 gauge. I
find a single sprue of about 10 ga works well but I cut it in such a
way that it necks down to a tiny opening just at the deepest point
of the depression. This is to preclude the metal from prematurely
breaking its surface tension and entering the sprue whilst heating
it. Steam casting is not for high capacity or large projects (though
some people might use it for that by developing special techniques).
I use it for single item casts or when I don’t want to take the time
to set up my centrifugal or vacuum systems. Don’t do much casting
these days, although I’m just in the midst of putting a course
together for the Boca Raton Museum of Art School and will begin
teaching casting in the March term.

By the way, for those Orchidians in South Florida, the Boca Raton
Museum of Art - The Art School has changed its name to - The Countess
Henrietta de Hoernle Art School.

Hope this helps. Cheers from Don at The Charles Belle Studio in SOFL
where simple elegance IS fine jewelry! @coralnut1


#4

I believe that it was in Tim McCreight’s book "Creative Casting"
where I read that you can reheat a flask as long as you let it cool
to room temperature, soak it in water to rehydrate it and then take
it back up to casting temperature. I can pull out the book and get
more details if anyone wants, but that, in short is what I have come
across.

Larry


#5

Rick:

I have had various kiln failures over the years during burnout. Of
course to repair the kiln, everything had to cool down including the
flasks. Each time I have had to deal with this disaster I would just
start the burnout over again and they always cast fine. I have always
read or been told that this is not possible so who knows, it worked
for me.

Ken Gastineau
Berea, Kentucky


#6

Hi Rick,

Just this week, due to a power outage just as I turned my kiln down
from 1350, I had to wait over 12 hours to cast. I simply brought my
temperature back up to casting temp, let it soak for an hour, and all
was good, no problem with the castings. I have had this occur on
several occasions and have never had a mold break or any other
adverse affect from having the flasks cool and then be reheated.
Good luck!

John


#7

Hello Casters, I thought I should weigh in on this one. Over the
years, I too have had kiln failures during burnout. They can happen
from switch, element, wiring or program failure, or even a power
outage just before casting. However, it is possible to get perfect
castings after an interrupted burnout or temp drop. There some things
to watch for though. It is NOT a good idea to water soak an already
burned out flask. The steam can break partially soaked investment.
The most important thing to do is let the flask temp change as slowly
as possible. Here’s a possible scenario and solution; Your kiln quits
at 900F on the way up and you don’t decide to do anything until it’s
at 800F, you discover the problem was another appliance on the same
circuit (not a good idea!) and you reset the circuit breaker. You can
turn the heat back up and continue to the top of the cycle. Another
possibility; The element has broken, the kiln you have doesn’t have
the element buried so you can see it right away. After some
expressive words, you close the kiln, unplug it and wait until the
next day. Carefully place the flask somewhere it won’t be jostled or
bumped, complete your kiln repair and start from the beginning with
your burnout. If this is going to be a week you can put the room
temp flask in a plastic bag until you’re ready to begin the second
burnout. If you have an auxiliary kiln on the bench, it can take over
after it has warmed up to the same temp as the flasks when they are
switched. Re-burning your flasks can be done successfully with the
flasks that were present during the problem run, but you should not
add newly invested flasks to the re-burn. Excessive moisture from the
newly introduced flasks can create some problems in the partially
burned flasks. This is probably where the idea to soak the 2nd burn
flasks came from. It is better to do a separate burnout for the new
ones later. The most important thing to remember is to prevent
thermal shock. Heating up or cooling down too fast will usually crack
the flask. Remember that the christobalite and silica are expanding
around 700F and need to hang out there for an hour or so, as with any
burnout. And speaking of burnout…I hope you got all your jobs done
and can relax and enjoy the celebration of our Saviors birth…Merry
Christmas from all the jewelry elves up here in Maine (we’re very
close to the north pole!) John, J.A.Henkel Co. Inc., Moldmaking
Casting Finishing, Producing Solutions for Jewelry Artists


#8
   I believe that it was in Tim McCreight's book "Creative
Casting" where I read that you can reheat a flask as long as you
let it cool to room temperature, soak it in water to rehydrate it
and then take it back up to casting temperature.  I can pull out
the book and get more details if anyone wants, but that, in short
is what I have come across. 
I have had my electric elements on my kiln burn out with a full

load, removed the flasks the kiln, had to let it cool down to
replace the elements, load up the kiln and reheat the load with no
negative consequences. I don’t even ramp the burnout, just put it on
1350 and let the mass of 6 3"by 7" flasks control how fast the kiln
heats up. With small flasks I would be more careful.


#9

I have had to reheat molds twice because of a failed oven. Both
times the molds were heated to about 800 degrees before the oven
failed. In one case I had to remove the molds and rebuild the oven
which allowed the molds to cool considerably. The other time
transferred the molds into a spare oven that was allowed to heat up
to about 400 degrees before the transfer was made. The castings in
both cases came out OK.

I guess that it would depend on the temperature the molds reached
before the cooling took place. If moisture in the mold is important
for proper burn out, the loss of some moisture before cooling and
reheating take place might cause failures.

Again I think that the status an artist has with the angels of
artistic creation has a lot of what works and what does not work.
If it doesn’t we would all be investing exactly the same way,
burning out at the same sequence, heating the metal to the exactly
the same temperature and pouring into molds of the exact same
temperature and quenching the metal at the same delay time after
pouring. I am just joking about the angels but we all have success
while using various times and temperatures. What work for one may
not work for another.


#10

Dear John, Rick & All, This happens at school all the time. If a
student doesn’t show up we pull the flask and try either the next day
or the next week depending on class schedule. You can leave the flask
at the casting temperature for quite a long time. I’ve had flasks at
casting temperature for two or three days and still cast
successfully. However, if they cool down to room temperature you do
have more concerns. Reheating smaller flasks spin casting give the
best results. Larger flasks (one & a half pounds of investment and
up) vacuum casting is very very risky. If you try with the vacuum, as
soon as you put the vacuum on, listen for a popping sound. If you
hear it, the flask has just blown out. This will leave an open path
for the molten metal to go through the flask and either into the
vacuum line, flask chamber or even vacuum pump. Most of the time the
molten metal just gets to the brass vacuum table fittings and freezes
up. All in all a lot of work. Not only lost metal but rebuilding a
vacuum system can be time consuming and expensive. Most of the stuff
we cast at school comes from molds so if we sacrifice a flask or two
to the casting Gods we can always do them again.

Best Regards,
Todd Hawkinson
T.R. the Teacher
www.trhawkinson.com
www.ajt-online.com
www.mctc.mnscu.edu/jewelry


#11

All, Been doing a bit of research on this subject and believe Larry
is correct…at least re the reheating aspect. Murry Bovin’s nice
little book, "Centrifugal or Lost Wax Jewelry Casting for Schools,
Tradesmen and Craftsmen mentions that a flask can be reheated
(slowly) to the proper casting temperature. Also, I did not finish my
thought in my last post re keeping flasks damp…like putting them
into a plastic bag overnight. Actually, after investing, they can be
kept for an indefinate time by letting them simply dry up. then,
rehydrate them by dipping in water or wrapping them in a moist towl.

Seems the moistness is very important because it seal the porous
walls of the burned out model and smooths the surface of the
cast…it also turns to steam during wax burn out and keeps the wax
from permeating the investment.

Not much scientific here but maybe a bit more info. Cheeers from
Don at The Charles Belle Studio in SOFL where simple elegance IS fine
jewelry! @coralnut1


#12

Hello Rick. You have probably already had to take action and I’m
late getting to this. For the future and for anyone else who has a
burn-out problem or casting delay, take heart.

Of first importance, be sure your burn-out was gradual and not too
hot at peak. Second, let the flasks cool down naturally and slowly,
by just turning off the kiln and cracking the door a bit. When they
can be touched, you can take them out and wrap them in a zip-baggie
with a wet paper towel. This will stabilize the drying out process.
When you know you can cast them, hopefully within a few days, but up
to a week has been done successfully, set your kiln to the desired
casting temp. Take your flasks and gently dunk in a pan of water
briefly. Gently is important in every step of handling burnt-out
flasks - no impact of any kind please. Place them in the kiln and
cast as soon as you know they have come to the correct temperature.
You should have no serious problem with this, assuming all your
investment mixtures and the first burn-out were ideal. The casting
gods seem to look with favor on our emergencies. This has been
necessary any number of times due to power-failures, human failures,
etc. with the casting at the school where I teach. Try to stay calm
and do everything right in spite of the delay. Your castings will
probably turn out just fine. All of ours were. Let me know how it
goes, or inquire further if necessary. Good luck.

Pat


#13
had to let it  cool down to replace the elements, 

By some coincidence, Orchidians are talking about kilns going out
and after 13 years of great service mine went out. It got up to
temp then when I checked back it was cooling down (casting came out
fine luckily!!). How do you determine if its the elements or
thermostat? Do you keep some on hand for emergency? Is fixing a 13
year old Kerr worth it or get a new one?

Thanks for any enlightenment! Marta


#14
 I believe that it was in Tim McCreight's book "Creative Casting"
where I read that you can reheat a flask as long as you let it
cool to room temperature, soak it in water to rehydrate it and then
take it back up to casting temperature. 

Just my .5-cents’ worth-- I don’t do a whole lot of casting, but I
have reheated flasks a number of times, for one reason or another.
One even got reheated twice. I didn;'t soak them, or do anything. So
far, they have come out fine…subject to change without notice.

–Noel


#15

When that has happen to me. I kept the door closed to the oven and
kept the heat in the chamber up to 24 hrs. changed the elements and
all was good. Andy “Tool Man” Kroungold TOOLS & SUPPLIES PHONE
800-877-7777 EXT 4194 FAX 337-262-7791


#16

When I taught casting there was a student that kept on promising to
show up to cast his flask. He kept missing class and then would
call the next day to make sure I put his flask in the oven. We went
through this for at least 6 classes before he arrived and cast his
piece. There were no problems. Another student had the flask burnt
out at least twice, then did not show up for a few months and wanted
the flask cast. That one worked well too. I always used Satin Cast
(no connection or endorsements). I don’t think that had much to do
with it. The class was in Chicago, not a very dry climate. Steve
Ramsdell


#17

Marta, It is definitely worth fixing, especially if it’s a Kerr.
There are several things that can malfunction and cause a no or low
heat problem. I had a door switch go once that slowed me down for a
day or so. The main switch can go as well and cause the same no heat
symptom. My Kerr furnace has three elements. It still heated (slowly)
with one element busted. After you unplug the kiln you can check all
the components with a fairly simple meter. If you don’t know
electricity, get a friend that (really) does. Gesswein is the closest
tool company to me that stocks or can get parts drop shipped to me
sometimes overnight. I have three different brand kilns. Maintenance
and repair is usually cheaper. John, J.A.Henkel Co., Inc.,
Moldmaking Casting Finishing, Producing Solutions for Jewelry
Artists