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De-Ox ster casting problem



 
 
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  #1  
Old October 29th 03, 04:16 AM
Mark
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Default De-Ox ster casting problem

Has anyone out there found a cure for rings cracking at the sprue when using
the De-ox sterling silver alloys.
I found a piece of info on the United Metals website that suggested a
"lighter" investment mix as it would be "not" as strong as the mud I usually
mix.
I like the de-ox for its anti firescale property's, but the shank cracks (
from hairline to complete cracked shanks at the sprue ) are a big problem.
So far I have tried .................
Regular sterling silver casting grain no problems.
Then comes the fun part.. switch to De-Ox grain and the problems start.

The lighter investment mix mentioned.
15{ normal} & 20 & 30 minute wait times before quenching the flasks.
At the 30 minute mark, there is almost no boil-off so I dig out the tree
with a screwdriver
Adding 2 extra sprues to the ring, pain in the *ss to clean up and no help
either.

I am using a kerr electro-melt with the built in temp controller so
over-temp is not a problem.
Casting temp is 1950 F per Rio Grande catalog. With the usual 50/50 mix of
new grain to sprue/button.
Flask temp is 1000 F for heavy stuff, 1100 F for medium stuff and 1200 F for
the fillagree type stuff.
Kerr Satin-cast 20 is investment.
My normal set-up is standard investment procedures with 1 hour setup, De-wax
in pre-boiling dewaxer, and into a pre-warmed kiln, ramp up temp 1400 and
down to casting with the usual times for heat soak prior to casting.
Thanks in advance !
Mark

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  #2  
Old October 29th 03, 04:47 PM
Heinrich Butschal
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Default

Mark wrote:
Has anyone out there found a cure for rings cracking at the sprue
when using the De-ox sterling silver alloys.
I found a piece of info on the United Metals website that suggested a
"lighter" investment mix as it would be "not" as strong as the mud I
usually mix.
I like the de-ox for its anti firescale property's, but the shank
cracks ( from hairline to complete cracked shanks at the sprue )
are a big problem. So far I have tried .................
Regular sterling silver casting grain no problems.
Then comes the fun part.. switch to De-Ox grain and the problems
start.


I am not shure what is your "de-ox". I suggest it is borax or boric acid.
In that case I have an explanation.
1. The grain is hydrophilic and so it contains normally a percentage of
water.
2. Silver and Gold alloys are able to dissolve enormous contents of
Hydrogen. Quite a lot of books are writing that silver dissolves an
enormous content of oxygen. This is possible, however I mentioned
in my praxis and in different tests, more evidence for soluted hydrogen.

Now, if you put your grain on top of the melted silver, the held water
will get separated in nascending Oxygen and nascending Hydrogen.
My experience is, that the nascending Hydrogen will be immediatly
absorbed by the fluid metal.
When the metal is cooling down and building new crystels, there is
less absorbing potential, so the gas will build vapor locks.

There are some solutions wich will work:
Roast your grain one time in the oven with a little bit over 280 °C
or put your grain into your melting pot before the silver is fluid, never
on top of the fluid metal.

If there is some alloy ruined by soluted gas, melt it severeal times
and pour it in a iron form under some fire on the surface.
So the gas bubbles, witch have no place between the crystals will
have some time to get out by the fluid surface.
In most cases three times is enough.
Alternatively you might use "degassing flux"
You find some more description how to use at my homepage he
http://www.butschal.de/werkstatt/solution.html

--
Heinrich Butschal
Forschung und Entwicklung, Goldschmiedemeister
http://manufactury.butschal.com




 




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