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Casting Problems


#1

hello out there, got a problem, This is my 3rd or so time to cast and
every time I fell,when I go to put the 4x3 1/2 flask on the vacume
cast I turn it on for it to vacume I hear it crack, but I go ahead
and pour the silver in any way.And when I emerge it in the bucket of
water to see if it came out , all the silver at the top of the
bracelet flashed,silver all around the top. Im wasting my time on
cleaning waxes and cast time. I get now were, Please help ,…:slight_smile:
it is a 4 by 3-1/2 flask I use 8oz of water and about 2 1/2 c of
powder.is that right? I put the flask in after I invested the night
before. at 300 then 700 then 1350 then back down to 900 and hold when
im ready to cast.Its 2 hrs for each temp. Thank you… BnH :slight_smile:


#2
And when I emerge it in the bucket of water to see if it came out ,
all the silver at the top of the 

I’ve done this myself. :slight_smile:

My experience has been that when you have a large flashing of metal
all around the top of the tree (the button being the bottom of the
tree), it may be that your waxes were too close to the top of the
flask. Leave a good 1/2" of space between the highest part of the
tree and top of the investment. If your model is particularly heavy,
you could leave even a bit more space. That 1/2" plus of investment
is needed for strength during casting. (Half an inch between the
outside of the tree and the sides of the flask doesn’t hurt either.)

Hope that helps.

Best Regards,

Elaine Corwin
Gesswein Co. Inc. USA


#3

Hola: The quantity of water should always be 40% of the powder, that
means for every 100 parts of Investment powder add 40 parts of water
(units does not matter as long as they are the same or equivalent).
Another important consideration is the time you spend mixing and
vaccuming. Most manufacturers recommend a total of nine minutes
because it is convenient to finish a couple of minutes before the
setting time, that normaly is around 12 minutes. Everybody is aware of
the problems of taking too long (the mixture hardens and you loose
definition or spoil all the work), but shortening the time is also a
problem because the powder separates and goes to the bottom of the
flask while the water goes to the top. This causes a very strong mold
at the bottom of the flask, but very weak at the top, with the
consecuences of water marks and cracking. The burning cycle seams good
enough.

David Duhne
Diamantex, M�xico


#4

Hi Bnh, I believe your problem may stem from the bracelet being too
close to the flask (minimum of 3/4")and possibly not enough head room
(from top of wax to top of flask, a bare minimum of one inch, more is
better). Not to worry, I have the solution. Go to the hardware store
and purchase 6" of fiberglass rope, the kind that is used on the door
of a wood stove. Use some stong shears and cut it all up into 1/4"
pieces. Mix all this into your powder before you add it to the water.
You may find you need a bit more water, have some handy to make the
investment pourable. I use this method for casting large things with
deep undercuts. You may want to use a power mixer to mix thoroughly.
This method adds the “rebar” to prevent cracking. You could also try
using a much larger flask and slow down your burnout. 2hrs @ 300F,
2hrs @ 500, 2 hrs @ 700, 2 hrs @ 1000 climb to 1350 hold for 2 hrs,
Don’t open the oven but let it cool to casting temp and hold 1hr.
John, J.A.Henkel Co., Moldmaking Casting Finishing


#5
   it is a 4 by 3-1/2  flask. I use 8oz of water and about 2 1/2 c
of powder. 

BnH,

The water to investment ratios are by weight, not volume. Mixing to
the ratio you are listing would not give a proper investment, which
probably is part of your problem. Using 8 oz. of water (1 cup) would
require 20 oz. be weight of investment (in standard ounces not troy.)
Spacing from the bottom of the flask is also important, especially
for large heavy pieces.

Allan Beck
Simmons Fine Jewelry
Boise, ID


#6

You may be using too much flux. I started out with a torch but
switched to a melting furnace. I use a lot of flux also but I play
with the molten metal before casting to remove as much of the flux
as possible. Use a graphite rod to puch the flux off to the side of
the metal surface and try to dip it out of the melt with the end of
the rod just before casting. Robert Hood