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Casting argentium silver


#1

Hi, I’ve been doing investment castings in sterling for a few years
and recently tried 935 argentium casting grain- resulting casting
was incredibly brittle and hard as woodpecker lips! Sprues (8 ga.)
snapped off easily with fingers, thin areas of casting began
cracking when glass beaded etc. and all were far to brittle to use.

These were approx, 3/8- 1/2" O.D. thin cup shaped castings. Metal
was poured a little under 1800F with Electro- melt into 2-1/2" flasks
with 700F flask temp., and allowed to air cool 15 mins before quench
and cleaning. Followed the argentium casting guidelines far as I
could tell… Does anything here sound way off?? Never experienced
anything like this with sterling on the same castings so wondering
what to do.


#2

Hello,

We have been casting Argentinum without any troubles that you
mentioned. We are using legor Argentinum. We use a closed system
Yasui Casting machine with pressure over vacuum. Check if you have
any contamination that can cause this. What system are you using for
casting? is it suitable for casting argentinum? How many times has
the argentinum metal used prior to this casting? Presently all I can
suggest is carry out a audit of the entire process. XRF analysis
will help. Do mail me I can help you in this regard.

Regards
Umesh


#3

If you are seeking no firescale and perfect castings. I highly
recomend #57

De ox sterling grain from United. I would also cast fasks much
hotter, flask 950 to 1050F metal temp 1850 quench 20 min. I also had
issues with Argentium. Great for rolling not so great for casting.
Just my 2 cents.

Alan


#4

Just wanted to say thanks for replies on casting argentium problem-
will try flask temp of 900-1000F next time with 25 min. cool down and
see what happens!

George


#5

Hi,

In addition to the temperature adjustments that were suggested by
Charles Allenden, I suggest that you try one of the Argentium Pro
alloys. I don’t do my own castings, but the folks that I know of
prefer the “Pro” casting alloys.

Cynthia Eid
http://www.cynthiaeid.com


#6

I too am having difficulty getting the vacuum casting down. Would
appreciate any tips, feedback or suggestions. Would be happy to send
an image of last nights casting tree to see if it is my spruing.

Last night was about my 20th casting attempt. Teaching myself
everything from books, videos, Utube and here.

Working shop temperature is 38-41 F if that makes a difference. Yes,
the F is for farenheit. It is winter here!

Argentium 935

Satin Cast 20

12 hour burn out with 60-90 minute hold at 1,000 degrees prior to
casting.

Electromelt at 1,830 degrees and holding about ten mintues to be
sure the crucible is hot all the way to the pour spout

Vacuum is about 24-25 drawdown when I pour.

About 15-20 seconds from the time the flask is placed on the pad to
pour. So maybe flask internal is cooling to 950?

Tonight I will try bumping temps up to 1,050 and 1,850

I am getting incomplete fills. The branch ends are rounded off. Bail
loops on pendants do not fill at all. Some pieces break off the
branch as being brittle. Flask size was 3x5 and I use a wet paper
towel between the flask and the silicone pad as that has increased
vacuum preasure.

I am using 1/3 old and 2/3 brand new grain. Allowing to air cool 3-5
hours (12 last night as it was late) and breaking out the investment
by hand with an awl, tiny screw driver and tooth brush.

Last nights cast I had two pieces almost complete at the base
towards the button. The day before it was two pieces at the very end
of the tree, but I had a vacuum problem that day.

The flasks are sanded as is the investment. I am using four brass
rods on the edge and leaving BE-1 inch of investment on the pull
side. I am treeing a mix trying to find the sweet spot for something.
Heavy pieces seem to fill better than the light pieces.

My first attempts were just one piece and in spite of all the
mistakes I was making, were ok even based mostly on gravity. I did
not know about the red silicone gasket sequence, vacuum importance,
seal importance, bubbles, etc.

Thank you
Charlie


#7

Hello Charlie,

The rounded ends that you describe on your incomplete castings are
classic signs of one of three main possible causes that you have
already identified:

  1. Low metal temperature
  2. Low flask temperature
  3. Not enough vacuum.

Your current metal temperature of 1830F is around what I would
recommend. Increasing this to 1850F is a sensible move as this should
increase the fluidity of the molten metal and increase fill. The one
thing you need to consider when looking at metal temperature is where
your thermocouple is situated to measure it. By this I mean is it in
the side of the crucible, in the central plunger or a direct reading
from immersion in a sheath in the molten metal. You will find that
your ‘standard’ metal temperature that you use to cast can vary by
about 40F from published recommendations dependent on how and where
the measurement is taken.

The flask temperature of 1000F also is around what I would
recommend. Higher flask temperatures certainly help with fill on
thinner sections and again it is a sensible increase that you propose
to 1050F. The only point I would make is that generally I would aim
to change only one temperature variable at a time (i.e. either flask
or metal) so that I could assess the impact that each different
individual change has on the quality of the castings. I know this is
a longer method and involves additional testing, but provided you
keep good notes about the size and weight of the castings you are
doing at each temperature it will give you a valuable set of casting
parameters for future work.

Finally the vacuum. You do not say in your post if you are located
at sea level or altitude. In general, at sea level a good vacuum pump
will pull down to 28-29 inches of mercury but a useful vacuum is
about 27 inches mercury. At higher altitudes the level that your
vacuum pump will pull down to will be a lower number in inches of
mercury.

If this problem does comes down to insufficient vacuum one possible
fix is to go for a slightly larger sprue size to get the molten metal
into the castings quicker and rely more on the molten metal pressure
in the sprues to assist with the fill.

I hope this helps you. Please let me know how you get on with your
next casts.

Charles Allenden
Argentium International


#8

Hello,

We cast using Yasui K3 Pressure over casting machine with auto
pouring facility. Our flask temperatures are 630 degrees centigrade
& casting temperatures are 980degrees centigrade. We are using Legor
Argentinum 935. We do not face any shortfills.

My suggestion woulf be increase the falsk temperature & observe. If
you still get shortfills check your alloy temp with the alloy
manufcturer. Check your vacuum pump is there full air displacement?
Start the vacuum ahead of casting allow some time for displcement of
air from the flask. What ratio are you using for investment is it
40:100 check it.

Umesh


#9

Hi Charles,

I had one other thought. I have seen differences in the amount of
time that a flask is out of the oven prior to the pour. If this
caster is still having issues after methodically incorporating all of
your suggestions, perhaps the time lag of the flask exposed to rather
cool room temps should be examined.

Just my 2 cents. (probably only worth 1 cent).o)
Regards,
Cliff


#10

I ended up finally getting a perfect cast. All bail loops of
pendants included. I did a mixed tree of heavy rings, pendants,
charms and smaller trees of fine bails. They all came out. So that
tells me it works for the fine things and I could cut back a bit for
heavier pieces.

The problem I had discovered is all my training books, videos, faqs
sheets from suppliers, websites and Utubes did not refer to there
being a difference in flask/pour temperatures from centrifugal verses
vacuum casting. I found a comment on it at United Metals Refinery.

I had been too conservative and was not understanding why I was
getting incompletes at the recommended 900 degrees, even after
pushing up to 1,000. And the pour should have been fine at 1,750 and
I pushed to 1,775.

After reading that vacuum casting requires 150-200 degrees
Fahrenheit higher temperatures, a light went off. I hurriedly
assembled a mix tree and held the flask at 1,175F and poured at
1,860F. I will experiment a little more as I’d like to bring the
temps down a little. Most that emailed seem to be around 1,100 and
1,800.

Also, Charles from Argentium mentioned sea level and that if I was
above, I would not get as much draw. I am 630 feet above sea level
and get to pull 25 and was waiting for 27-28. I pour within 15
seconds of flask removal and draw to 25 before pouring. And 40/100
ratio for investment.

The only other thing I cannot figure out right now is the bottom of
the tree is black whereas the top and button are pure silvery white.
Any thoughts on that one?

Regarding the Tungsten Disulfide, I have a batch of Argentium
pendants tumbling for 24 hours in coarse walnut shell and then will
do another 24-36 hours in fine walnut shell. Both with .5 micron
Tungsten Disulfide. If it seems like it does anything I will then
try polishing a piece with the .1 micron and Picasso blue to see if
it does anything. I’m hoping for a super slippery effect and even
more resistance to tarnish. If it works, I’ll send a piece to
Charles at Argentium to test as it’s his baby.

Charlie at Seawear


#11
The only other thing I cannot figure out right now is the bottom
of the tree is black whereas the top and button are pure silvery
white. Any thoughts on that one? 

Longer burnout and/or better circulation of air in the kiln. You
still have carbon in the mold.

James Binnion
James Binnion Metal Arts


#12
From Charlie at Seawear: I ended up finally getting a perfect
cast. 

Yay! Great to hear. Good for you for persisting. Thanks for letting
us know.

Cynthia Eid
http://www.cynthiaeid.com


#13
Longer burnout and/or better circulation of air in the kiln. You
still have carbon in the mold. 

He also doesn’t mention what his actual maximum burnout temperature
is, only the end flask temperatures at casting. The burnout needs to
get substantially hotter, normally somewhere around 1300 to a max
(for satin cast) of 1350, in order to eliminate all the carbon. If at
lower temperatures, then it may need to be there for much longer…

Peter


#14
He also doesn't mention what his actual maximum burnout temperature
is, only the end flask temperatures at casting. The burnout needs 
to get substantially hotter, normally somewhere around 1300 to a
max (for satin cast) of 1350, in order to eliminate all the carbon.
If  at lower temperatures, then it may need to be there for much
longer... 

At temperatures of 1300-1350 the gypsum binder in the investment
begins to break down if there is carbon present and begins to
produce sulfur dioxide. This can lead to gas porosity issues. So
longer burnout times at lower temps (1250F) will reduce the
likelihood of gas porosity.

James Binnion
James Binnion Metal Arts


#15

Hello Charlie,

Glad that you are now getting successful castings. With regard to
the dark deposit on the bottom of your tree; I agree with Jim Binnion
that this is most likely related to poor burn out of the wax and some
carbon residue being left in the flask as you cast.

It sometimes helps to think of the burn out oven as an incinerator
and what you want to remove is the wax. This then comes down to two
simple requirements, time at temperature and good air flow around the
flask during the burn out cycle. The base of the burn out oven should
be grooved to allow wax to flow away from the flask and air to flow
into the flask. If the bottom of the oven is not grooved then raising
the flask slightly on some ceramic pieces will allow good air flow
into the flask.

Another tell-tale sign of poor burnout (lack of air flow) is a
yellow ring of sulphur present on the investment powder by the button
after casting.

I am more than happy to look at any cast pieces for you - best of
luck with the polishing.

Charles Allenden
Argentium International


#16
He also doesn't mention what his actual maximum burnout
temperature is, only the end flask temperatures at casting. The
burnout needs to get substantially hotter, normally somewhere
around 1300 to a max (for satin cast) of 1350, in order to
eliminate all the carbon. If at lower temperatures, then it may
need to be there for much longer... 

Sorry, it is 1,350 for three hours. Satin Cast 20.

The next one I will leave the air vent open all the way for entire
burn out. I am steaming the flask for 45 minutes and putting into the
oven once it reaches 260 degrees.

Made a new graphite vacuum pad and anxious to try it out. Got a
vacuum pull of 26 with just my finger plugging the hole!

Still learning!

Charlie


#17

Have you worked with Sterlium Plus from Stuller?